Note: Descriptions are shown in the official language in which they were submitted.
CA 02405648 2002-09-27
-1-
LUBRICATING OIL COMPOSITIONS
The present invention concerns improved lubricating oil compositions for
residual
fuel oil-fuelled diesel engines. In particular, the present invention concerns
lubricating oil compositions that demonstrate improved cylinder liner wear
performance.
In large diesel engines of the cross-head type used in marine and heavy
io stationary applications, the cylinders are lubricated separately from the
other
engine components. The cylinders are lubricated on a total loss basis with the
cylinder oil being injected separately to quills on each cylinder by means of
lubricators positioned around the cylinder liner. Oil is distributed to the
lubricators
by means of pumps, which are, in modern engine designs, actuated to apply the
is oil directly onto the rings to reduce wastage of the oil. The high stresses
encountered in these engines and the use of residual fuels creates the need
for
lubricants with a high detergency and neutralising capability even though the
oils
are exposed to thermal and other stresses only for short periods of time.
Residual
fuels commonly used in these diesel engines typically contain significant
quantities
20 of sulfur, which, in the combustion process, combine with water to form
sulfuric
acid, the presence of which leads to corrosive wear. In particular, in two-
stroke
engines for ships, areas around the cylinder liners and piston rings can be
corroded and worn by the acid. Therefore, it is important for diesel engine
lubricating oils to have the ability to resist such corrosion and wear.
The art describes the use of particular additives to neutralise the sulfuric
acid
formed and thus protect the cylinder liners and piston rings from corrosion
and
wear.
3o For example, US-A-4842755 discloses the use of borated dispersants and zinc
dialkyldithiophosphates in a marine cylinder lubricating oil composition to
provide
anti-wear performance in the cylinder liner and piston ring areas.
CA 02405648 2002-09-27
_2.
US-A-4948522 discloses marine diesel cylinder lubricants comprising a borated
dispersant and a polybutene, and optionally a zinc dialkyldithiophosphate
andlor
an overbased metal detergent. The lubricants have improved ring wear and
linear
wear performance and good protection against corrosion.
US-A-6140280 discloses succinimide compounds that exhibit corrosion resistance
and wear resistance in diesel engines. It also discloses that conventional
anti-
wear agents, such as zinc dithiophosphates and molybdenum dithiocarbamates,
may be used as co-additives.
to
WO 99/64543 discloses cylinder oils of defined characteristics and a liquid
polyisobutylene. The cylinder oils provide improved performance including
protection against corrosive, friction and abrasive wear.
is The aim of the present invention is to provide a lubricating oil
composition that
offers effective cylinder liner protection, particularly in the areas of the
cylinder that
are prone to corrosive wear.
Accordingly, in a first aspect, the present invention provides a lubricating
oil
2o composition for a residual fuel oil-fuelled diesel engine for marine and
stationary
applications, comprising:
(a) an oil of lubricating viscosity, in a major amount; and
(b) an oil-soluble or oil-dispersible molybdenum compound, in a minor
2s ~ amount;
wherein the oil composition has a TBN from 20 to 100 as measured according to
ASTM D-2896 and a viscosity at 100°C in the range from 9 to 30 mm2
s -' as
measured according to ASTM D-445.
In a second aspect, the present invention provides a combination of a cylinder
of a
two-stroke cross-head marine diesel engine and a lubricating oil composition
of
the first aspect, wherein the cylinder is characterised by a power output of
4000 or
CA 02405648 2005-12-20
-3-
greater, such as~4200 or greater, preferably 4500 or greater, more preferably
in
the range of 4500 to 6000, kW.
In a third aspect, the present invention provides the use of an oil-soluble or
oil-
dispersible molybdenum compound or a composition, such as an oleaginous
composition, comprising the molybdenum compound, to reduce corrosive wear in
a cylinder liner of a residual fuel oil-fuelled diesel engine, preferably a
cross-head
marine engine.
io In a fourth aspect, the present invention provides a method of reducing
corrosive
wear in a cylinder liner of a residual fuel oil-fuelled diesel engine,
preferably a
cross-head marine, comprising supplying to the walls of the cylinder a
lubricating
oil composition of the first aspect.
is In a fifth aspect, the present invention provides an additive composition
comprising:
(a) an oil-soluble or oil-dispersible molybdenum compound; and
(b) one or more co-additives;
2o wherein the additive composition contains (a) and (b) in an amount to
provide a
lubricating oil composition having a TBN from 20 to 100 as measured according
to ASTM D-2896 and a viscosity at 100°C in the range from 9 to 30 mm2
s'' as
measured according to ASTM D-445, when the lubricating oil composition
contains 5 to 40 mass % of the additive composition.
2s
In another aspect, there is provided a lubricating oil composition for a
residual
fuel oil-fuelled diesel engine for marine and stationary applications,
comprising:
(a) an oil of lubricating viscosity, in an amount in excess of 50% of the oil
composition; (b) an oil soluble or oil-dispersible trinuclear molybdenum
3o compound, in an amount less than 50% of the oil composition; and (c) a
detergent composition, which comprises one or more overbased metal
CA 02405648 2005-12-20
-3 a-
detergents; wherein the oil composition has a TBN from 30 to 100 as
measured according to ASTM D-2896 and a viscosity at 100°C in the range
from 9 to 30 mm2s' as measured according to ASTM D-445.
In this specification, the following words and expressions shall have the
meanings ascribed below:
"major amount" means in excess of 50 mass % of the
composition, preferably in excess of 60 mass %, more
preferably in excess of 70 mass %, and most preferably in
excess of 80 mass %;
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"minor amount" means less that 50 mass % of the composition, preferably
less than 40 mass %, more preferably less than 30 mass %, and most
preferably less than 20 mass %, both in respect of the stated additive and
in respect of the total mass % of all the additives present in the lubricant,
s reckoned as active ingredient of the additive or additives;
"active ingredient (a.i.)" refers to additive material that is not diluent or
solvent.
io "comprises or comprising" or cognate words specifies the presence of
stated features, steps, integers or components, but does not preclude the
presence or addition of one or more other features, steps, integers,
components, or groups thereof;
~s "TBN" - Total Base Number as measured by ASTM D2~396;
"oil-soluble or oil-dispersible" - does not necessarily indicate solubility,
dissolvability, miscibility or capability of suppression in oil in all
proportions.
They do mean, however, solubility or stable dispersibility sufficient to exert
2o the intended effect in the environment in which the oil is employed.
Moreover, additional incorporation of other additives may permit
incorporation of higher levels of a particular additive, if desired.
It will be understood that the various components of the lubricating oil
2s composition, essential as well as optimal and customary, may react under
the
conditions of formulation, storage or use and that the invention also provides
the
product obtainable or obtained as a result of any such reaction.
The features of the invention will now be discussed in more detail below.
Diesel Engines
Diesel fuel oils can in general be divided into two main categories -
distillates and
heavy or residual fuels. Distillates consist of one or more distillate
fractions.
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Heavy or residual fuels are fuels that comprise at least a proportion of a
residual
oil, i.e. oil that remains after the distilled fractions have been removed
from
unrefined oil. The composition of the residual fuel will vary with the
composition of
the starting oil, usually a crude oil, and will also vary depending upon the
s distillation conditions. However, by its nature, residual fuel oil is of
high molecular
weight, contains significant quantities of sulfur and has a high boiling
point. The
term "residual oil" is understood by those skilled in the art; it is defined
according
to the standards ISO 8217, ISO RME25 and ISO RME35.
io The present invention is suitable for large residual fuel oil-fuelled
diesel engines,
such as diesel engines of the cross-head type used in marine and heavy
stationary applications, and of the trunk piston type found in marine
applications.
Large diesel engines are mainly employed for marine propulsion and power
generation. Diesel engines suitable in the present invention can also be
fuelled
Is by a mixture of distillate and residual fuels.
Cross-head engines tend to be two-stroke, whereas trunk piston engines tend to
be four-stroke. Four-stroke trunk piston engines may have a speed of 100 to
2,000, preferably 300 to 1,800, more preferably 350 to 1500, rpm, and the
cylinder
2o is characterised by power output of 50 to 10000, preferably 100 to 6000,
more
preferably 150 to 5000, kW. Two-stroke cross-head engines may have a speed of
40 to 600, preferably 60 to 500, such as 80 to 300, rpm and the cylinder is
characterised by a power output of 4000 or greater, such as 4200 or greater,
preferably 4500 or greater, more preferably in the range of 4500 to 6000, kW.
2s Further, the engines may, for example, have from 6 to 12 cylinders and
their total
output may, for example, be in the range of 18,000 to 70,000 kW. The bore of
the
cylinder may, for example, be 850 or greater, such as 900 or greater,
preferably in
the range of 900 to 1000, cm.
3o The lubricating oil compositions of the present invention are particularly
useful in
cross-head engines, such as two-stroke cross-head engines for marine
propulsion
and stationary power generation.
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Lubricating Oil Composition
In respect of each aspect of the present invention, the total base number
(TBN) of
the lubricating oil composition, independent of the viscosity at 100
°C, is preferably
30 to 95, more preferably 40 to 90, even more preferably 65 to 90.
In respect of each aspect of the present invention, the viscosity at 100
°C of the
lubricating oil composition, independent of the TBN, is preferably 9 to 25,
more
preferably 12 to 25, even more preferably 16 to 25, such as 18 to 22, mm2 s-'.
to In respect of each aspect of the present invention, the viscosity index, as
defined
by ASTM D2270, of the lubricating oil composition is preferably at least 90,
more
preferably at least 95, especially at least 100, for example in the range from
90 to
110.
is Lubricating oil compositions used in large residual-fuelled diesel
~.~ngines can
become contaminated with residual fuel during use, particularly in four-stroke
trunk piston engines. Therefore, the lubricating oil compositions of the
invention
can also contain a residual fuel oil.
2o The lubricating oil compositions of the present invention will typically be
monograde, i.e. compositions that exhibit little or no viscosity index
improvement
properties, for example, an SAE30, SAE 40, SAE 50 or higher lubricant. Thus,
lubricating oil compositions of the present invention preferably do not
comprise a
viscosity index modifier.
Oil of Lubricating Viscosity
The oil of lubricating viscosity (sometimes referred to as lubricating oil)
may be
any oil suitable for the lubrication of a large diesel engine, such as a cross-
head
engine or a trunk piston engine. The lubricating oil may suitably be an
animal, a
3o vegetable or a mineral oil. Suitably the lubricating oil is a petroleum-
derived
lubricating oil, such as a naphthenic base, paraffinic base or mixed base oil.
Alternatively, the lubricating oil may be a synthetic lubricating oil.
Suitable
synthetic lubricating oils include synthetic ester lubricating oils, which
oils include
CA 02405648 2002-09-27
diesters such as di-octyl adipate, di-octyl sebacate and tri-decyl adipate, or
polymeric hydrocarbon lubricating oils, for example liquid polyisobutene and
poly-
alpha olefins. Commonly, a mineral oil is employed.
s Another class of lubricating oils is hydrocracked oils, where the refining
process
further breaks down the middle and heavy distillate fractions in the presence
of
hydrogen at high temperatures and moderate pressures. Hydrocracked oils
typically have kinematic viscosity at 100 °C of from 2 to 40, for
example from 3 to
15, mm2s-' and a viscosity index typically in the range of from 100 to 110,
for
io example from 105 to 108.
The term 'brightstock' as used herein refers to base oils which are solvent-
extracted, de-asphalted products from vacuum residuum, which generally have a
kinematic viscosity at 100 °C of from 28 to 36 mm2s-' and are typically
used in a
is proportion of less than 30, preferably less than 20, more preferably less
than 15,
most preferably less than 10, such as less than 5, mass %, based on the mass
of
the lubricating oil composition.
Molybdenum Compound
2o Molybdenum compounds suitable in the present invention include any oil-
soluble
or oil-dispersible molybdenum compounds, such as organic molybdenum
compounds.
Examples of organic molybdenum compounds include molybdenum xanthates,
2s thioxanthates, alkoxides, carboxylates, dialkyldithiocarbamates,
dialkyldithiophosphinates and dialkyldithiophosphates.
The molybdenum compound may, for example, be mononuclear, dinuclear,
trinuclear or tetranuclear. The molybdenum compound is preferably polynuclear
30 (e.g. trinuclear or tetranuclear).
binuclear molybdenum compounds can be represented by the formula
CA 02405648 2002-09-27
_g_
MoOXS4_xL2, where L is a ligand such as dialkyldithiocarbamate and
dialkyldithiophosphate, and x is an integer from 0 to 4. An example of
dinuclear
(or dimeric) molybdenum dialkyldithiocarbamate is expressed by the following
formula:
Ri S Xt X2 Xa S R3
\N / \ ~~ / \~~ / '\ /
/ C\~ / M ~ / M ~ ~ N\
R2 S X3 S R4
where R~ to R4 independently denote a straight chain, branched chain or
aromatic
hydrocarbyl group having 1 to 24 carbon atoms; and X~ to X4 independently
denote an oxygen atom or a sulfur atom. The four hydrocarbyl groups, R~ to R4,
to may be identical or different from one another.
Another group of organo-molybdenum compounds useful in the lubricating
compositions of this invention are trinuclear (or trimeric) molybdenum
compounds,
especially those of the formula Mo3SkL~QZ and mixtures thereof, wherein the L
are
is independently selected ligands having organo groups with a sufficient
number of
carbon atoms to render the compound soluble in the oil, n is from 1 to 4, k
varies
from 4 to 7, Q is selected from the group of neutral electron donating
compounds
such as water, amines, alcohols, phosphines, and ethers, and z ranges from 0
to
5 and includes non-stoichiometric values. At least 21 total carbon atoms
should
2o be present among all the ligands' organo groups, such as at least 25, at
least 30,
or at least 35 carbon atoms.
The ligands may be selected from the group consisting of
X~ X~ R
-X-R 1, X$ 2, Xz 3,
CA 02405648 2002-09-27
_g_
x' ~ -~I /' x' ~ ~ ~t
Xs ~z 4 xz ~ ~s 5
and mixtures thereof, wherein X, X,, X2, and Y are selected from the group
consisting of oxygen and sulfur, and wherein R~, R2, and R are selected from
s hydrogen and organo groups that may be the same or different. Preferably,
the
organo groups are hydrocarbyl groups such as alkyl (e.g., in which the carbon
atom attached to the remainder of the ligand is primary or secondary), aryl,
substituted aryl and ether groups. More preferably, each ligand has the same
hydrocarbyl group.
io
The term "hydrocarbyl" as used herein denotes a substituent having carbon
atoms
directly attached to the remainder of the ligand and is predominantly
hydrocarbyl
in character. Such substituents include the following:
is 1. Hydrocarbon substituents, that is, aliphatic (fc~r example alkyl or
alkenyl), alicyclic (for example cycloalkyl or cycloalkenyl) substituents,
aromatic-, aliphatic- and alicyclic-substituted aromatic nuclei, as well as
cyclic substituents wherein the ring is completed through another portion of
the ligand (that is, any two indicated substituents may together form an
2o alicyclic group).
2. Substituted hydrocarbon substituents, that is, those containing non-
hydrocarbon groups which do not alter the predominantly hydrocarbyl
character of the substituent. Those skilled in the art will be aware of
suitable
2s groups (e.g., halo, especially chloro and fluoro, amino, alkoxyl, mercapto,
alkylmercapto, vitro, nitroso, sulfoxy, etc.).
Importantly, the organo groups of the ligands have a sufficient number of
carbon
atoms to render the compound soluble in the oil. For example, the number of
3o carbon atoms in each group will generally range between 1 to 100,
preferably from 1
to 30, and more preferably between 4 to 20. Preferred ligands include
CA 02405648 2002-09-27
-10-
dialkyldithiophosphate, alkylxanthate, carboxylates, dialkyldithiocarbamate
("dtc"),
and mixtures thereof. Most preferred are the dialkyldithiocarbamates. Those
skilled
in the art will realize that formation of the compounds of the present
invention
requires selection of ligands having the appropriate charge to balance the
core's
s charge (as discussed below).
Compounds having the formula Mo3SkL~Qz have cationic cores surrounded by
anionic ligands, wherein the cationic cores are represented by structures such
as
8 ~ ~B 8 ~ ~"''~6
_S ~ -S
Mo / M /o
1
1o 1, and 2,
which have net charges of +4. Consequently, in order to solubilize these cores
the total charge among all the ligands must be -4. Four monoanionic ligands
are
preferred. Without wishing to be bound by any theory, it is believed that two
or
is more trinuclear cores may be bound or interconnected by means of one or
more
ligands and the li_gands may be multidentate, i.e., having multiple
connections to
one or more cores. It is believed that oxygen and/or selenium may be
substituted
for sulfur in the core(s).
2o Oil-soluble trinuclear molybdenum compounds can be prepared by reacting in
the
appropriate liquid(s)/solvent(s) a molybdenum source such as
(NH4)2Mo3S~3~n(H20), where n varies between 0 and 2 and includes non-
stoichiometric values, with a suitable ligand source such as a
tetralkylthiuram
disulfide. Other oil-soluble trinuclear molybdenum compounds can be formed
2s during a reaction in the appropriate solvents) of a molybdenum source such
as
(NH4)ZMo3S,3w(H20), a ligand source such as tetralkylthiuram disuitide,
dialkyldithiocarbamate, or dialkyldithiophosphate, and a sulfur-abstracting
agent
such as cyanide ions, sulfite ions, or substituted phosphines. Alternatively,
a
CA 02405648 2002-09-27
trinuclear molybdenum-sulfur halide salt such as [M']2[Mo3S~A6], where M' is a
counter ion, and A is a halogen such as CI, Br, or I, may be reacted with a
ligand
source such as a dialkyldithiocarbamate or dialkyldithiophosphate in the
appropriate liquid(s)/solvent(s) to form an oil-soluble trinuclear molybdenum
s compound. The appropriate liquid/solvent may be, for example, aqueous or
organic.
The ligand chosen must have a sufficient number of carbon atoms to render the
compound soluble in the lubricating composition.
to
Trinuclear molybdenum compounds for use in the compositions of this invention
can be those of the formula Mo3S7((aikyl)2dtc)4 where the alkyl has about 8 to
18
carbon atoms. The alkyl is preferably a "coco" alkyl chain which is a mixture
of
chains of varying even numbers of carbon atoms from typically a C8 to C~$
alkyl,
is mainly Coo, C~2 and C,4 alkyls derived from coconut oil.
Other examples of molybdenum compounds include a sulfurized molybdenum
containing composition prepared by (i) reacting an acidic molybdenum compound
and a basic nitrogen compound selected from the group consisting of
succinimide,
2o a carboxylic acid amide, a hydrocarbyl monoamine, a phosphoramide, a
thiophosphoramide, a Mannich base, a dispersant viscosity index improver, or a
mixture thereof, ~in the presence of a polar promoter, to form a molybdenum
complex, and (ii) reacting the molybdenum complex with a sulfur-containing
compound, to thereby form a sulfur- and molybdenum-containing composition.
In one embodiment of the present invention, the molybdenum compound is
preferably trinuclear.
In another embodiment of the present invention, the molybdenum compound,
3o irrespective of its nuclearity, is preferably fully sulfurised, i.e. the
core contains
only sulfur, for example Mo2S4, Mo3S4 and Mo3S~.
CA 02405648 2005-12-20
-12-
In another embodiment of the present invention, the molybdenum compound is
preferably a dithiocarbamate compound, such a trinuclear molybdenum
dithiocarbamate; especially effective compounds are molybdenum
dialkyldithiocarbamate compounds represented by the formula
Mo3S~((alkyl)2dtc)4.
In each aspect the of present invention, the lubricating oil composition
preferably
contains 5 to 5000, more preferably 10 to 1000, especially 50 to 750, ppm of
molybdenum by mass, based on the mass of the oil composition. In one
embodiment, the molybdenum compound is present in an amount from 1 to
io 10,000 ppm.
Oil-soluble or oil-dispersible molybdenum compounds, such as trinuclear
molybdenum dithiocarbamates, have been found to be particularly effective in
preventing corrosive wear in the cylinder liner.
is
The amount of molybdenum is measured according to ASTM D5185.
Dispersant
In respect of each aspect of the invention, the lubricating oil compositions
can also
2o comprise a dispersant. Dispersants maintain oil-insoluble substances,
resulting
from oxidation during use, in suspension in the fluid, thus preventing sludge
flocculation and precipitation or deposition on metal parts.
So-called ashless dispersants are organic materials, which form substantially
no
2s ash on combustion, in contrast to metal-containing (and thus ash-forming)
detergents. Borated metal-free dispersants are regarded herein as ashless
dispersants.
Typically, the dispersants comprise amine, alcohol, amide, or ester polar
moieties
3c~ attached to the polymer backbone often via a bridging group. The
dispersant may
be, for example, selected from oil-soluble salts, esters, amino-esters,
amides,
imides, and oxazolines of long chain hydrocarbon substituted mono- and
dicarboxylic acids or their anhydrides; thiocarboxylate derivatives of long
chain
CA 02405648 2005-12-20
-12a-
hydrocarbons; long chain aliphatic hydrocarbons having a polyamine attached
directly thereto; and Mannich condensation products formed by condensing a
long
CA 02405648 2002-09-27
-13-
chain substituted phenol with formaldehyde and polyalkylene polyamine, and
Koch reaction products.
The polymer backbone is typically an olefin polymer, especially polymers
s comprising a major molar amount (i.e. greater than 50 mole %) of a C2 to C,$
olefin (e.g., ethylene, propylene, butylene, isobutylene, pentene, octene-1,
styrene), and typically a C2 to C5 olefin. The oil-soluble polymeric
hydrocarbon
backbone may be a homopolymer (e.g., polypropylene or polyisobutylene) or a
copolymer of two or more of such olefins (e.g., copolymers of ethylene and an
Io alpha-olefin such as propylene and butylene or copolymers of two different
alpha-
olefins).
One preferred class of olefin polymers is polybutenes and specifically
polyisobutenes (PIB) or poly-n-butenes, such as may be prepared by
is polymerization of a C4 refinery stream. Another preferred class of olefin
polymers
is ethylene alpha-olefin (EAO) copolymers or alpha-olefin homo- and copolymers
such as may be prepared using metallocene chemistry having in each case a high
degree (e.g. >30%) of terminal vinylidene unsaturation.
2o The polymer backbone wiN usually have number average molecular weight (Mn)
within the range of from 100 to 20,000 or 10,000. The M n of the backbone is
preferably within the range of 250 or 500 to 10,000, more preferably 700 to
5,000.
Both relatively low molecular weight (Mn 500 to 1500) and relatively high
molecular weight (Mn 1500 to 5,000 or greater) polymers are useful to make
2s dispersants. Particularly useful olefin polymers for use in dispersants
have Mn
within the range of from 900 to 3000. The olefin polymers used to prepare
dispersants preferably have approximately one terminal double bond per polymer
chain.
3o Suitable dispersants include, for example, derivatives of long chain
hydrocarbon-
substituted carboxylic acids in which the hydrocarbon groups contain 50 to 400
carbon atoms, examples of such derivatives being derivatives of high molecular
weight hydrocarbyl-substituted succinic acid. Such hydrocarbyl-substituted
CA 02405648 2002-09-27
-14-
carboxylic acids may be reacted with, for example, a nitrogen-containing
compound, advantageously a polyalkylene polyamine, or with an ester.
Particularly preferred dispersants are the reaction products of polyalkylene
amines
with alkenyl succinic anhydrides. Examples of specifications disclosing
s dispersants of the last-mentioned type are US-A-3 202 678, 3 154 560, 3 172
892,
3 024 195, 3 024 237, 3 219 666, 3 216 936 and BE-A-662 875.
The dispersant can be further post-treated by a variety of conventional post
treatments such as boration, as generally described in US 3,087,936 and
Io 3,254,025. This is readily accomplished by treating an acyl nitrogen-
containing
dispersant with a boron compound selected from the group consisting of boron
oxide, boron halides, boron acids and esters of boron acids or highly borated
low
Mw dispersant, in an amount to provide a boron to nitrogen mole ratio of 0.01 -
5Ø Usefully the dispersants contain from 0.05 to 2.0, e.g. 0.05 to 1.5 or
0.9,
is mass % of boron based on the total mass (active ingredient basis) of the
borated
acyl nitrogen compound.
Preferred for use in the invention is a polyisobutenyl succinimide dispersant
wherein the Mn of the polyisobutenyl groups is from 750 to 3000, such as 900
to
20 1200 or 2000 to 2300.
In one embodiment of the present invention, the amount of dispersant, based on
nitrogen derived from the dispersant, in the lubricating oil composition is
preferably
up to 1.0, more preferably 0.001 to 0.08, such as 0.005 to 0.55 or 0.50, mass
%,
2s based on the mass of the lubricating oil composition.
In another embodiment of the present invention, the amount of dispersant,
based
on boron derived from the dispersant, in the lubricating oil composition is
preferably not more than 0.5, such as not more than 0.25, for example 0.005 to
30 0.1, mass %, based on the mass of the lubricating oil composition.
Preferably the dispersant is a borated dispersant, such as a borated
succinimide.
CA 02405648 2002-09-27
-15-
The amount of boron is measured according to ASTM D5185; the amount of
nitrogen is measured according to ASTM D5291; the M n can be determined by
several known techniques - a convenient method for such determination is by
gel
permeation chromatography (GPC) which additionally provides molecular weight
s distribution information.
Detergent
In respect of each aspect of the invention, the lubricating oil compositions
can also
comprise a detergent composition, which comprises one or more detergents,
1o preferably overbased detergents.
A detergent is an additive that reduces formation of piston deposits, for
example
high-temperature varnish and lacquer deposits, in engines; it has acid-
neutralising
properties and is capable of keeping finely divided solids in suspension. It
is
~s based on metal "soaps", that is metal salts of acidic organic compounds,
sometimes referred to as surfactants.
Large amounts of a metal base can be included by reacting an excess of a metal
compound, such as an oxide or hydroxide, with an acidic gas such as carbon
2o dioxide to give an overbased detergent which comprises neutralised
detergent as
the outer layer of a metal base (e.g. carbonate) micelle.
The metals can be selected from Group 1 and Group 2 metals, e.g., sodium,
potassium, lithium, calcium, and magnesium. Calcium and magnesium are
2s preferred; more preferably the metal is calcium.
Surfactants that may be used include organic carboxylates, for example,
aliphatic
carboxylates and aromatic carboxylates, such as salicylates, non-sulfurised or
sulfurised; sulfonates; phenates, non-sulfurised or sulfurised;
thiophosphonates;
3o and naphthenates.
CA 02405648 2002-09-27
-16-
Examples of suitable detergents include overbased metal phenates, metal
sulfonates, metal salicylates and metal carboxylates, where the metal is
selected
from sodium, calcium and magnesium; preferably the metal is calcium.
s Also suitable in each aspect of the present invention is a detergent in the
form of a
hybrid complex detergent, wherein the basic material is stabilised by more
than
one type of surfactant (see WO 97/46643, WO 97/46644, WO 97/46646, and WO
97/46647). It will be appreciated by one skilled in the art that a single type
of
organic acid may contain a mixture of organic acids of the same type. For
io example, a sulphonic acid may contain a mixture of sulphonic acids of
varying
molecular weights. Such an organic acid composition is considered as one type.
Thus, complex detergents are distinguished from mixtures of two or more
separate overbased detergents, an example of such a mixture being one of an
overbased salicylate detergent with an overbased phenate detergent.
is
The art describes examples of overbased complex detergents. For example,
International Patent Application Publication Nos. 9746643/4/5/6 and 7 describe
hybrid complexes made by neutralising a mixture of more than one acidic
organic
compound with a basic metal compound, and then overbasing the mixture.
2o Individual basic micelles of the detergent are thus stabilised by a
plurality of
surfactant types.
EP-A-0 750 659 describes a calcium salicylate phenate complex made by
carboxylating a calcium phenate and then sulfurising and overbasing the
mixture
2s of calcium salicylate and calcium phenate. Such complexes may be referred
to as
"phenalates"
Surfactants for the surfactant system of the overbased metal detergent may
contain at least one hydrocarbyl group, for example, as a substituent on an
3o aromatic ring. Advantageously, hydrocarbyl groups in surfactants for use in
accordance with the invention are aliphatic groups, preferably alkyl or
alkylene
groups, especially alkyl groups, which may be linear or branched. The total
CA 02405648 2002-09-27
-17-
number of carbon atoms in the surfactants should be at least sufficient to
impact
the desired oil-solubility.
The proportion of one detergent type (e.g. calcium sulfonate) to another
detergent
s type (e.g. sodium phenate) in the detergent composition is not critical.
Similarly,
the proportion of one surfactant to another in a complex detergent is not
critical.
The detergent composition may comprise a major proportion of a phenate
detergent or comprises a complex hybrid detergent having a major proportion of
a
to phenate surfactant, where the phenate detergent or the complex hybrid
detergent
is preferably a calcium salt.
The overbased detergents of the present invention may have a TBN of at least
200, preferably at least 250, especially at least 300, such as up to 600.
The lubricating oil compositions of the present invention have a sufficient
amount
of additives, for example, detergents, whether neutral or overbased, to
provide the
required TBN. For example, the detergent composition may be used up to 30,
preferably 2 to 15 or to 20, mass % of detergent composition, based on the
mass
of the lubricating oil composition.
Co-Additives
The lubricants may include an antiwear agent as a co-additive and may also
contain other co-additives, for example, antioxidants, antifoaming agents
and/or
2s rust inhibitors. Further~details of particular co-additives are as follows.
Oxidation inhibitors, or antioxidants, reduce the tendency of mineral oils to
deteriorate in service, evidence of such deterioration being, for example, the
production of varnish-like deposits on metal surfaces and of sludge, and
viscosity
3o increase. Suitable oxidation inhibitors include sulphurized alkyl phenols
and alkali
or alkaline earth metal salts thereof; diphenylamines; phenyl-naphthylamines;
and
phosphosulphurized or sulphurized hydrocarbons.
CA 02405648 2002-09-27
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Other oxidation inhibitors or antioxidants that may be used in the lubricant
comprise oil-soluble copper compounds. The copper may be blended therein as
any suitable oil-soluble copper compound. By oil-soluble is meant that the
compound is oil-soluble under normal blending conditions in the base stock or
an
s additive package. The copper may, for example, be in the form of a copper
dihydrocarbyl thio- or dithio-phosphate. Alternatively, the copper may be
added
as the copper salt of a synthetic or natural carboxylic acid, for example, a
C8 to
C18 fatty acid, an unsaturated acid, or a branched carboxylic acid. Also
useful are
oil-soluble copper dithiocarbamates, sulphonates, phenates, and
io acetylacetonates. Examples of particularly useful copper compounds are
basic,
neutral or acidic copper Cu l and/or Cu II salts derived from alkenyl succinic
acids
or anhydrides.
Additional detergents and metal rust inhibitors include the metal salts, which
may
is be overbased and have a TBN less than 300, of sulphonic acids, alkyl
phenols,
sulphurized alkyl phenols, alkyl salicylic acids, thiophosphonic acids,
naphthenic
acids, and other oil-soluble mono- and dicarboxylic acids. Representative
examples of detergents/rust inhibitors, and their methods of preparation, are
given
in EP-A-208 560. In the case of metal salts of salicylic acids, the TBN of the
metal
2o salts may be less than 200.
Antiwear agents, as their name implies, reduce wear of metal parts. Zinc
dihydrocarbyl dithiophosphates (ZDDPs) are very widely used as antiwear
agents.
Especially preferred ZDDPs are those of the formula Zn[SP(S)(OR~)(OR2)]2
2s wherein R~ and R2 represent hydrocarbyl groups such as alkyl groups that
contain
from 1 to 18, preferably 2 to 12, carbon atoms. Also suitable are ashless or
non-
metal containing additives, such as sulfur and/or phosphorus containing
compounds, for example, sulfurised phenol and amine dithiophosphate.
3o The oil compositions of the present invention may contain 0 to 0.2,
preferably 0.05
to 0.15, more preferably 0.01 to 0.1, mass % of phosphorus, based on the mass
of
the oil composition. In a preferred embodiment of the present invention, the
oil
CA 02405648 2002-09-27
-19-
composition contains less than 150, preferably less than 100, more preferably
less
than 50, for example 0, ppm of phosphorus.
Pour point depressants, otherwise known as tube oil flow improvers, lower the
s minimum temperature at which the fluid will flow or can be poured. Such
additives
are well known. Foam control may be provided by an antifoamant of the
polysiloxane type, for example, silicone oil or polydimethyl siloxane.
Typical proportions for additives for a four-stroke trunk piston engine oil
io composition are as follows:
Additive Mass % a.i Mass % a.i.*
*
(Broad) (Preferred)
Detergents) 0.5-10 2-7
Dispersant(s) 0.5-5 1-3
Anti-wear agents) 0.1-1.5 0.5-1.3
Oxidation inhibitor 0.2-2 0.5-1.5
Rust inhibitor 0.03-0.15 0.05-0.1
Pour point depressant 0.03-0.15 0.05-0.1
Mineral or synthetic base Balance Balance
oil
* Mass % active ingredient based on the final oil composition.
Typical proportions for additives for a two-stroke cross-head oil composition
are as
is follows:
Additive Mass % a.i.* Mass % a.i
(Broad) (Preferred)
Detergents) 1-18 3-12
Dispersant(s) 0.5-5 1-3
Anti-wear agents) 0.1-1.5 0.5-1.3
Pour point depressant 0.03-0.15 0.05-0.1
Mineral or synthetic base Balance Balance
oil
* Mass % active ingredient based on the final oil composition.
When a plurality of additives is employed it may be desirable, although not
2o essential, to prepare one or more additive compositions (also known as
packages)
CA 02405648 2002-09-27
-20-
or concentrates comprising the additives, whereby several additives can be
added
simultaneously to the oil of lubricating viscosity to form the lubricant or
lubricating
oil composition. Dissolution of the additive packages) into the oil of
lubricating
viscosity may be facilitated by solvents and by mixing accompanied with mild
s heating, but this is not essential. The additive packages) will typically be
formulated to contain the additives) in proper amounts to provide the desired
concentration, and/or to carry out the intended function, in the final
lubricant when
the additive packages) is/are combined with a predetermined amount of oil of
lubricating viscosity.
to
Thus, the molybdenum compound in accordance with the present invention may
be admixed with small amounts of base oil or other compatible solvents
together
with other desirable additives to form additive packages containing active
ingredients in an amount, based on the additive package, of, for example, from
2.5
is to 90 and preferably from 5 to 75 and most preferably from 8 to 60, mass %,
the
remainder being base oil or other compatible solvents.
The lubricating oil composition may typically contain 5 to 40, preferably 10
to 38,
more preferably 16 to 34, mass °!o of the additive package(s), based on
active
Zo ingredient.
The present invention is illustrated by, but in no way limited to, the
following
examples.
CA 02405648 2002-09-27
-21-
Examples
Lubricating oil compositions were prepared by methods known in the art. Table
1
shows the compositional details of Example 1 and Comparative Examples 1 and
s 2. Example 1 and Comparative Examples 1 & 2 were blended so that the
resulting lubricating oil composition has a TBN of 70 and viscosity at
100°C of
about 20 mm2s'.
Example 1, an example according to the present invention, is a lubricating oil
to composition comprising 550 ppm of molybdenum; Comparative Examples 1 and 2
contain the same detergents and dispersant as Example 1, but Comparative
Example 1 contains a zinc dithiophosphate additive instead of the molybdenum
compound and Comparative Example 2 does not contain the molybdenum
compound or the zinc compound. Comparative Example 3 is a commercial
is lubricating oil composition having a TBN of 70 and viscosity at
100°C of about 20
mm2s''.
The lubricating oil compositions of Example 1 and Comparative Examples 1 to 3
were tested for cylinder liner wear performance in a slow speed two-stroke
cross-
2o head "Bolnes" engine. Such engines are widely used by those skilled in the
art for
lubricating performance evaluation such as disclosed in a presentation by
Nippon
Mitsubishi Oil Company on 10 May 2001 at CIMAC conference entitled "The
influence of the neutralisation ability of marine lubricants on engine
lubrication"
Takeshmia et al.
The cylinder liner wear data for Example 1 and Comparative Examples 1 to 3 are
provided in Table 2. The data shows that Example 1 provides better wear
protection than any one of Comparative Examples 1 to 3, in particular better
than
Comparative Example 1, which contains ZDDP. This improvement is especially
3o evident in positions 2 to 5 of the cylinder.
CA 02405648 2002-09-27
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