Note: Descriptions are shown in the official language in which they were submitted.
USE OF POLYISOBUTYLENE IN A LUBRICANT TO REDUCE DEPOSIT
FORMATION IN A MARINE DIESEL ENGINE
FIELD OF THE INVENTION
This invention concerns reducing deposit formation in a centrifuge system in a
trunk piston diesel engine.
BACKGROUND OF THE INVENTION
Trunk piston diesel engines are used in marine, power generation and rail
traction applications and may have a rated speed of between 300 and 1000 rpm.
In
trunk piston diesel engines, a single lubricant composition is used for
crankcase and
cylinder lubrication. All major moving parts of the engine, i.e. the main and
big end
bearings, camshaft and valve gear, are lubricated by a pumped circulation
system. The
cylinder liners are lubricated partially by splash lubrication and partially
by oil from the
circulation system which finds its way to the cylinder wall through holes in
the piston
skirt via the connecting rod and gudgeon pin.
Trunk piston diesel engines use a centrifuge system to remove contaminants
such as, for example, soot or water, from the lubricant composition. The
centrifuge
system relies on the use of a sealing medium that is heavier than the
lubricant. The
sealing medium is generally water. When the lubricant composition passes
through the
centrifuge system, it comes into contact with the water. The lubricant
therefore needs to
be capable of shedding the water and remaining stable in the presence of
water. If the
lubricant is unable to shed the water, the water builds up in the lubricant
forming an
emulsion, which leads to deposits building up in the centrifuge system and
prevents the
centrifuge system from working properly. The centrifuge system normally
operates at
temperatures of less than 100 C, such as less than 95 C, e.g. around 90 C.
Traditional trunk piston diesel engine lubricant compositions have a total
base
number of 30-40. However, the recent development of trunk piston diesel
engines
having very low oil consumption has resulted in lubricant formulators
increasing the
CA 2799383 2018-12-28
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total base number up to, for example, 50-60. Unfortunately, this increase in
total base
number affects the ability of the lubricant composition to shed any
contamination with
the sealing medium used in the centrifuge systems, resulting in deposits
building up in
the centrifuge system.
The aim of the present invention is to provide for the reduction of deposit
formation in a centrifuge system in a trunk piston diesel engine.
US-A-2008/0287329 Al ("329") describes a lubricant oil for a marine four-
stroke engine that includes I to 20 % by weight of at least one
polyisobutylene. '329
states that the increase of viscosity of such lubricant oils is slowed down.
However,
'329 makes no mention of the above-mentioned deposit formation problem in the
centrifuge of trunk piston engines.
SUMMARY OF THE INVENTION
It is now found that a polyisobutylene additive in a trunk piston engine oil
lubricant enables the above deposit formation to be overcome.
Thus, the present invention provides the use of a polyisobutylene of number-
average molecular weight in the range of 400 to 8000, such as 1,300 to 2,225,
and
having a kinematic viscosity at 100 C in the range of 50 to 50,000, such as
630 to
2,500, mm2/sec, as an additive constituting 1-25 mass % of a trunk piston
diesel
engine lubricant composition to reduce deposit formation in a centrifuge in a
trunk
piston diesel engine when the composition is lubricating the engine during its
operation.
Preferably, the trunk piston diesel engine lubricant composition contains
little
or no brightstock. Preferably, the trunk piston diesel engine lubricant
composition is
substantially free of brightstock. Even more preferably, the trunk piston
diesel engine
lubricant composition contains no brightstock.
In this specification, the following words and expressions, if and when used,
have the meanings ascribed below:
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CA 02799383 2012-12-20
"active ingredients" or "(a.i.)" refers to additive material that is not
diluent or
solvent;
"comprising" or any cognate word specifies the presence of stated features,
steps, or integers or components, but does not preclude the presence or
addition of one or more other features, steps, integers, components or groups
thereof; the expressions "consists of' or "consists essentially of' or
cognates
may be embraced within "comprises" or cognates, wherein "consists
essentially of' permits inclusion of substances not materially affecting the
characteristics of the composition to which it applies;
"major amount" means 50 mass % or more of a composition;
"minor amount" means less than 50 mass % of a composition;
"TBN" means total base number as measured by ASTM D2896.
Furthermore in this specification, if and when used:
"calcium content" is as measured by ASTM 4951;
"phosphorus content" is as measured by ASTM D5185;
"sulphated ash content" is as measured by ASTM D874:
"sulphur content" is as measured by ASTM D2622;
"KV100" means kinematic viscosity at 100 C as measured by ASTM D445.
Also, it will be understood that various components used, essential as well as
optimal and customary, may react under conditions of formulation, storage or
use and
that the invention also provides the product obtainable or obtained as a
result of any
such reaction.
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CA 02799383 2012-12-20
Further, it is understood that any upper and lower quantity, range and ratio
limits set forth herein may be independently combined.
DETAILED DESCRIPTION OF THE INVENTION
The features of the invention will now be discussed in more detail below.
OIL OF LUBRICATING VISCOSITY
The lubricant of composition contains a major proportion of an oil of
lubricating viscosity. Such lubricating oils may range in viscosity from light
distillate
mineral oils to heavy lubricating oils. Generally, the viscosity of the oil
ranges from 2
to 40, such as 3 to 15, mm2/scc, as measured at 100 C, and a viscosity index
of 80 to
100, such as 90 to 95. The lubricating oil may comprise greater than 60,
typically
greater than 70. mass % of the composition.
The oil may include 'brightstock' which refers to base oils which are solvent-
extracted, de-asphalted products from vacuum residuum generally having a
kinematic
viscosity at 100 C of from 28 to 36 mm2s-I. It is, however, preferred that
little or no
brightstock is included, for example less than 5, 4, 3, 2 or 1 mass %, based
on the
mass of the composition. Brightstock may be completely or substantially
absent.
Natural oils include animal oils and vegetable oils (e.g., castor oil, lard
oil);
liquid petroleum oils and hydrorefined, solvent-treated or acid-treated
mineral oils of
the paraffinic, naphthenic and mixed paraffinic-naphthenic types. Oils of
lubricating
viscosity derived from coal or shale also serve as useful base oils.
Synthetic lubricating oils include hydrocarbon oils and halo-substituted
hydrocarbon oils such as polymerized and interpolymerized olefins (e.g.,
polybutylcnes, polypropylenes, propylene-isobutylene copolymers, chlorinated
polybutylenes, poly(1-hexenes), poly(1-octenes), poly(1-decenes));
alkybenzenes (e.g.,
dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes, di(2-
ethylhexyl)benzenes);
polyphenyls (e.g., biphenyls, terphenyls, alkylated polyphenols); and
alkylated
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diphenyl ethers and alkylated diphenyl sulphides and derivative, analogues and
homologues thereof.
Alkylene oxide polymers and interpolymers and derivatives thereof where the
terminal hydroxyl groups have been modified by esterification, etherification,
etc.,
constitute another class of known synthetic lubricating oils. These are
exemplified by
polyoxyalkylene polymers prepared by polymerization of ethylene oxide or
propylene
oxide, and the alkyl and aryl ethers of polyoxyalkylene polymers (e.g., methyl-
polyiso-propylene glycol ether having a molecular weight of 1000 or diphenyl
ether
of poly-ethylene glycol having a molecular weight of 1000 to 1500); and mono-
and
polycarboxylic esters thereof, for example, the acetic acid esters, mixed C3-
C8 fatty
acid esters and Ci3 oxo acid diester of tetraethylene glycol.
Another suitable class of synthetic lubricating oils comprises the esters of
dicarboxylic acids (e.g., phthalic acid, succinic acid, alkyl succinic acids
and alkenyl
succinic acids, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric
acid,
adipic acid, linoleic acid dimer, malonic acid, alkylmalonic acids, alkenyl
malonic
acids) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl
alcohol,
2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether, propylene
glycol).
Specific examples of such esters includes dibutyl adipate, di(2-ethylhexyl)
sebacate,
di-n-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate,
dioctyl
phthalate, didecyl phthalate, dieicosyl scbacate, the 2-ethylhcxyl diester of
linoleic
acid dimer, and the complex ester formed by reacting one mole of sebacic acid
with
two moles of tetraethylene glycol and two moles of 2-ethylhexanoic acid.
Esters useful as synthetic oils also include those made from C5 to C12
monocarboxylic acids and polyols and polyol esters such as neopentyl glycol,
trimethylolpropane, pentaerythritol, dipentaerythritol and tripentaerythritol.
Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy- or
polyaryloxysilicone oils and silicate oils comprise another useful class of
synthetic
lubricants; such oils include tetraethyl silicate, tetraisopropyl silicate,
tetra-(2-
ethylhexyl)silicate, tetra-(4-methyl-2-ethylhexyl)silicate, tetra-(p-tert-
butyl-phenyl)
silicate, hexa-(4-methyl-2-ethylhexyl)disiloxane, poly(methyl)siloxanes and
CA 02799383 2012-12-20
poly(methylphenyl)siloxanes. Other synthetic lubricating oils include liquid
esters of
phosphorus-containing acids (e.g., tricresyl phosphate, trioctyl phosphate,
diethyl
ester of decylphosphonic acid) and polymeric tetrahydrofurans.
Unrefined, refined and re-refined oils can be used in lubricants of the
present
invention. Unrefined oils are those obtained directly from a natural or
synthetic
source without further purification treatment. For example, a shale oil
obtained
directly from retorting operations; petroleum oil obtained directly from
distillation; or
ester oil obtained directly from esterification and used without further
treatment are
unrefined oils.
POLYISOBUTYLENE
The polyisobutylene additive may be present in the following proportions: 1
to 20, or 1 to 15, such as 1-10, such as 1-6, such as 1-5, such as 1-4 mass
percent.
As mentioned above, the polyisobutylene has a number-average weight in the
range of 400 to 8,000, such as 1,300 to 2,225. Among other ranges that may be
used,
the following may be mentioned: 900 ¨ 3,000, 1,000 ¨ 8,000, 1,500 ¨ 6,000 and
2,000 ¨ 5,000, and also a lower limit of 500.
Also, the polyisobutylcne has a kinematic viscosity at 100 C in the range of
50
to 50,000, such as 630 to 2,500, mm2/sec. Among other ranges that may be used,
the
following may be mentioned: 2,000 ¨ 6,000, 2,000 ¨ 5,000, and 3,000 ¨ 4,500,
mm2/stc. Polyisobutylene also embraces mixtures of several polyisobutylenes,
synthesised separately and possibly having molecular weights outside the
ranges of
values indicated above, provided that the mixture of the various
polyisobutylenes has
a molecular weight lying within said ranges.
Polyisobutylene is commercially available.
CO-ADDITIVES
One or more of the following may also be indicated in the composition.
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Detergents
A detergent is an additive that reduces formation of 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 based on
metal "soaps", that is metal salts of acidic organic compounds, sometimes
referred to
as surfactants.
A detergent comprises a polar head with a long hydrophobic tail. Large
amounts of a metal base are included by reacting an excess of a metal
compound,
such as an oxide or hydroxide, with an acidic gas such as carbon dioxide to
give an
overbased detergent which comprises neutralised detergent as the outer layer
of a
metal base (e.g. carbonate) micelle.
The detergent is preferably an alkali metal or alkaline earth metal additive
such as an overbased oil-soluble or oil-dispersible calcium, magnesium, sodium
or
barium salt of a surfactant selected from phenol, sulphonic acid, carboxylic
acid,
salicylic acid and naphthenic acid, wherein the overbasing is provided by an
oil-
insoluble salt of the metal, e.g. carbonate, basic carbonate, acetate,
formate, hydroxide
or oxalate, which is stabilised by the oil-soluble salt of the surfactant. The
metal of
the oil-soluble surfactant salt may be the same or different from that of the
metal of
the oil-insoluble salt. Preferably the metal, whether the metal of the oil-
soluble or oil-
insoluble salt, is calcium.
The TBN of the detergent may be low, i.e. less than 50 mg KOH/g, medium,
i.e. 50-150 mg KOH/g, or high, i.e. over 150 mg KOH/g, as determined by ASTM
D2896. Preferably the TBN is medium or high, i.e. more than 50 TBN. More
preferably, the TBN is at least 60, more preferably at least 100, more
preferably at
least 150, and up to 500, such as up to 350 mg KOH/g, as determined by ASTM
D2896.
Surfactants for the surfactant system of the overbased detergent preferably
contain at least one hydrocarbyl group, for example, as a substituent on an
aromatic
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CA 02799383 2012-12-20
ring. The term "hydrocarbyl" as used herein means that the group concerned is
primarily composed of hydrogen and carbon atoms and is bonded to the remainder
of
the molecule via a carbon atom but does not exclude the presence of other
atoms or
groups in a proportion insufficient to detract from the substantially
hydrocarbon
characteristics of the group. Advantageously, hydrocarbyl groups in
surfactants for
use in accordance with the invention arc aliphatic groups, preferably alkyl or
alkylene
groups, especially alkyl groups, which may be linear or branched. The total
number
of carbon atoms in the surfactants should be at least sufficient to impart the
desired
oil-solubility.
Phenols, for use in preparing the detergents may be non-sulphurized or,
preferably, sulphurized. Further, the term "phenol" as used herein includes
phenols
containing more than one hydroxyl group (for example, alkyl catechols) or
fused
aromatic rings (for example, alkyl naphthols) and phenols which have been
modified
by chemical reaction, for example, alkylene-bridged phenols and Mannich base-
condensed phenols; and saligenin-type phenols (produced by the reaction of a
phenol
and an aldehyde under basic conditions).
Preferred phenols may be derived from the formula
OH
\I
where R represents a hydrocarbyl group and y represents 1 to 4. Where y is
greater
than I, the hydrocarbyl groups may be the same or different.
The phenols are frequently used in sulphurized form. Sulphurized
hydrocarbyl phenols may typically be represented by the formula:
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CA 02799383 2012-12-20
OH OH
=
x
Ry
where x is generally from 1 to 4. In some cases, more than two phenol
molecules
may be linked by Sx bridges.
In the above formulae, hydrocarbyl groups represented by R are
advantageously alkyl groups, which advantageously contain 5 to 100, preferably
5 to
40, especially 9 to 12, carbon atoms, the average number of carbon atoms in
all of the
R groups being at least 9 in order to ensure adequate solubility in oil.
Preferred alkyl
groups are nonyl (tripropylene) groups.
In the following discussion, hydrocarbyl-substituted phenols will for
convenience be referred to as alkyl phenols.
A sulphurizing agent for use in preparing a sulphurized phenol or phenate may
be any compound or element which introduces -(S)õ- bridging groups between the
alkyl phenol monomer groups, wherein x is generally from 1 to about 4. Thus,
the
reaction may be conducted with elemental sulphur or a halide thereof, for
example,
sulphur dichloride or, more preferably, sulphur monoehloride. If elemental
sulphur is
used, the sulphurization reaction may be effected by heating the alkyl phenol
compound at from 50 to 250, preferably at least 100, C. The use of elemental
sulphur will typically yield a mixture of bridging groups -(S)x- as described
above. If
a sulphur halide is used, the sulphurization reaction may be effected by
treating the
alkyl phenol at from ¨10 to 120, preferably at least 60, C. The reaction may
be
conducted in the presence of a suitable diluent. The diluent advantageously
comprises a substantially inert organic diluent, for example mineral oil or an
alkane.
In any event, the reaction is conducted for a period of time sufficient to
effect
substantial reaction. It is generally preferred to employ from 0.1 to 5 moles
of the
alkyl phenol material per equivalent of sulphurizing agent.
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Where elemental sulphur is used as the sulphurizing agent, it may be desirable
to use a basic catalyst, for example, sodium hydroxide or an organic amine,
preferably
a heterocyclic amine (e.g., morpholine).
Details of sulphurization processes are well known to those skilled in the
art.
Regardless of the manner in which they are prepared, sulphurized alkyl
phenols useful in preparing overbased detergents generally comprise diluent
and
unreacted alkyl phenols and generally contain from 2 to 20 mass %, preferably
4 to 14
mass %, and most preferably 6 to 12 mass%, sulphur based on the mass of the
sulphurized alkyl phenol.
As indicated above, the term "phenol" as used herein includes phenols that
have been modified by chemical reaction with, for example, an aldehyde, and
Mannich base-condensed phenols.
Aldehydes with which phenols may be modified include, for example,
formaldehyde, propionaldehyde and butyraldehyde. The preferred aldehyde is
formaldehyde. Aldehyde-modified phenols suitable for use are described in, for
example, US-A-5 259 967.
Mannich base-condensed phenols are prepared by the reaction of a phenol, an
aldehyde and an amine. Examples of suitable Mannich base-condensed phenols are
described in GB-A-2 121 432.
In general, the phenols may include substituents other than those mentioned
above provided that such substituents do not detract significantly from the
surfactant
properties of the phenols. Examples of such substituents are methoxy groups
and
halogen atoms.
Salicylic acids used in accordance with the invention may be non-sulphurized
or sulphurized, and may be chemically modified and/or contain additional
substituents,
for example, as discussed above for phenols. Processes similar to those
described
above may also be used for sulphurizing a hydrocarbyl-substituted salicylic
acid, and
CA 02799383 2012-12-20
are well known to those skilled in the art. Salicylic acids are typically
prepared by the
carboxylation, by the Kolbe-Schmitt process, of phenoxides, and in that case,
will
generally be obtained (normally in a diluent) in admixture with uncarboxylated
phenol.
Preferred substituents in oil-soluble salicylic acids from which overbased
detergents in accordance with the invention may be derived are the
substituents
represented by R in the above discussion of phenols. In alkyl-substituted
salicylic
acids, the alkyl groups advantageously contain 5 to 100, preferably 9 to 30,
especially
14 to 20, carbon atoms.
Sulphonic acids used in accordance with the invention are typically obtained
by sulphonation of hydrocarbyl-substituted, especially alkyl-substituted,
aromatic
hydrocarbons, for example, those obtained from the fractionation of petroleum
by
distillation and/or extraction, or by the alkylation of aromatic hydrocarbons.
Examples include those obtained by alkylating benzene, toluene, xylene,
naphthalene,
biphenyl or their halogen derivatives, for example, chlorobenzene,
chlorotoluene or
chloronaphthalene. Alkylation of aromatic hydrocarbons may be carried out in
the
presence of a catalyst with alkylating agents having from 3 to more than 100
carbon
atoms, such as, for example, haloparaffins, olefins that may be obtained by
dehydrogenation of paraffins, and polyolefins, for example, polymers of
ethylene,
propylene, and/or butene. The alkylaryl sulphonic acids usually contain from 7
to 100
or more carbon atoms. They preferably contain from 16 to 80, or 12 to 40,
carbon
atoms per alkyl-substituted aromatic moiety, depending on the source from
which
they are obtained.
When neutralizing these alkylaryl sulphonic acids to provide sulphonates,
hydrocarbon solvents and/or diluent oils may also be included in the reaction
mixture,
as well as promoters and viscosity control agents.
Another type of sulphonic acid that may be used in accordance with the
invention comprises alkyl phenol sulphonic acids. Such sulphonic acids can be
sulphurized. Whether sulphurized or non-sulphurized these sulphonic acids are
11
believed to have surfactant properties comparable to those of sulphonic acids,
rather than
surfactant properties comparable to those of phenols.
Sulphonic acids suitable for use in accordance with the invention also include
alkyl
sulphonic acids, such as alkenyl sulphonic acids. In such compounds the alkyl
group
suitably contains 9 to 100, advantageously 12 to 80, especially 16 to 60,
carbon atoms.
Carboxylic acids that may be used in accordance with the invention include
mono- and dicarboxylic acids. Preferred monocarboxylic acids are those
containing 1 to
30, especially 8 to 24, carbon atoms. (Where this specification indicates the
number of
carbon atoms in a carboxylic acid, the carbon atom(s) in the carboxylic
group(s) is/are
included in that number.) Examples of monocarboxylic acids are iso-octanoic
acid,
stearic acid, oleic acid, palmitic acid and behenic acid. Iso-octanoic acid
may, if desired,
be used in the form of the mixture of C8 acid isomers sold by Exxon Chemicals
under the
trade name CekanoicTM. Other suitable acids are those with tertiary
substitution at the
a-carbon atom and dicarboxylic acids with more than 2 carbon atoms separating
the
carboxylic groups. Further, dicarboxylic acids with more than 35, for example,
36 to
100, carbon atoms are also suitable. Unsaturated carboxylic acids can be
sulphurized.
Although salicylic acids contain a carboxylic group, for the purposes of the
present
invention they are considered to be a separate group of surfactants, and are
not considered
to be carboxylic acid surfactants. (Nor, although they contain a hydroxyl
group, are they
considered to be phenol surfactants.)
Examples of other surfactants which may be used in accordance with the
invention include the following compounds, and derivatives thereof: naphthenic
acids,
especially naphthenic acids containing one or more alkyl groups,
dialkylphosphonic
acids, dialkylthiophosphonic acids, and dialkyldithiophosphoric acids, high
molecular
weight (preferably ethoxylated) alcohols, dithiocarbamic acids,
thiophosphines, and
dispersants. Surfactants of these types are well known to those skilled in the
art.
Surfactants of the hydrocarbyl-substituted carboxylalkylene-linked phenol
type, or
dihydrocarbyl esters of alkylene dicarboxylic acids, the alkylene group being
substituted with a hydroxy group and an additional carboxylic acid group, or
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alkylene-linked polyaromatic molecules, the aromatic moieties whereof comprise
at
least one hydrocarbyl-substituted phenol and at least one carboxy phenol, may
also be
suitable for use in the present invention; such surfactants are described in
EP-A-708
17L
Further examples of detergents useful in the present invention are optionally
sulphurized alkaline earth metal hydrocarbyl phenates that have been modified
by
carboxylic acids such as stearic acid, for examples as described in EP-A- 271
262
(LZ-Adibis); and phenolates as described in EP-A- 750 659 (Chevron).
Also suitable for use in the present invention arc overbased metal compounds,
preferably overbased calcium detergents, that contain at least two surfactant
groups,
such as phenol, sulphonic acid, carboxylic acid, salicylic acid and naphthenic
acid,
that may be obtained by manufacture of a hybrid material in which two or more
different surfactant groups are incorporated during the overbasing process.
Examples of hybrid materials are an overbased calcium salt of surfactants
phenol and sulphonic acid; an overbased calcium salt of surfactants phenol and
carboxylic acid; an overbased calcium salt of surfactants phenol, sulphonic
acid and
salicylic acid; and an overbased calcium salt of surfactants phenol and
salicylic acid.
In the instance where at least two overbased metal compounds are present, any
suitable proportions by mass may be used, preferably the mass to mass
proportion of
any one overbased metal compound to any other metal overbased compound is in
the
range of from 5:95 to 95:5; such as from 90:10 to 10:90; more preferably from
20:80
to 80:20; especially from 70:30 to 30:70; advantageously from 60:40 to 40:60.
The hybrid detergent preferably includes at least 5 mass% of salicylate, more
preferably at least 10 mass% of salicylate. The hybrid detergent preferably
includes
at least 5 mass% of phenate. The amount of salicylate and phenate in the
hybrid
detergent can be determined using techniques such as chromatography,
spectroscopy
and/or titration, well known to persons skilled in the art. The hybrid
detergent may
also include other surfactants such as sulphonate, sulphurized phenate,
thiophosphate,
naphthenate, or oil-soluble carboxylate. The hybrid detergent may include at
least 5
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CA 02799383 2012-12-20
mass% of sulphonate. The surfactant groups are incorporated during the
overbasing
process.
Particular examples of hybrid materials include, for example, those described
in WO-A- 97/46643; WO-A- 97/46644; WO-A- 97/46645; WO-A- 97/46646; and
WO-A- 97/46647.
By an "overbased calcium salt of surfactants" is meant an overbased detergent
in which the metal cations of the oil-insoluble metal salt are essentially
calcium
cations. Small amounts of other cations may be present in the oil-insoluble
metal salt,
but typically at least 80, more typically at least 90, for example at least
95, mole %, of
the cations in the oil-insoluble metal salt, are calcium ions. Cations other
than
calcium may be derived, for example, from the use in the manufacture of the
overbased detergent of a surfactant salt in which the cation is a metal othcr
than
calcium. Preferably, the metal salt of the surfactant is also calcium.
Preferably, the TBN of the hybrid detergent is at least 300 mg KOH/g, such as
at least 330 mg KOH/g, more preferably at least 350 mg KOH/g, more preferably
at
least 400 mg KOH/g, most preferably in the range of from 400 to 600 mg KOH/g,
such as up to 500 mg KOH/g, as determined by ASTM D2896.
Preferably, the amount of overbased metal detergent in the lubricant is at
least
0.5, preferably in the range of from 5 to 50, more preferably from 10 to 50,
mass %
based on the total amount of the lubricant composition.
The overbased metal detergents may or may not be borated, and typically the
boron contributing compound, e.g the metal borate, is considered to form part
of the
overbasing. The detergent may include both a non-borated detergent and a
borated
detergent.
The overbased metal detergents preferably have a sulphated ash content (as
determined by ASTM D874) of at least 0.85%, more preferably at least 1.0% and
even more preferably at least 1.2%.
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The detergent or detergents may include phenol as an unreacted component
and, if so, the amount of phenol contributes to the total phenol content
present in the
trunk piston diesel engine lubricant composition. All of the phenol present in
the
trunk piston diesel engine lubricant composition may come from the detergent
or
detergents.
The trunk piston engine oil preferably also includes at least one dispersant,
anti-wear additive or anti-oxidant.
Dispersants
The trunk piston diesel engine lubricant composition may include at least one
dispersant. A dispersant is an additive for a lubricating composition whose
primary
function is to improve engine cleanliness.
A noteworthy class of dispersants are "ashless", meaning a non-metallic
organic material that forms substantially no ash on combustion, in contrast to
metal-
containing, hence ash-forming, materials. Ashless dispersants comprise a long
chain
hydrocarbon with a polar head, the polarity being derived from inclusion of,
e.g. an 0,
P or N atom. The hydrocarbon is an oleophilie group that confers oil-
solubility,
having for example 40 to 500 carbon atoms. Thus, ashless dispersants may
comprise
an oil-soluble polymeric hydrocarbon backbone having functional groups that
are
capable of associating with particles to be dispersed.
Examples of ashless dispersants are succinimides, e.g. polyisobutene succinic
anhydride; and polyamine condensation products that may be borated or
unborated.
If present, the dispersant is preferably present in an amount from 0.5 to 5
mass %, based on the total amount of the lubricant composition.
CA 02799383 2012-12-20
Anti-wear Additive
The trunk piston diesel engine lubricant composition may include at least one
anti-wear additive. The anti-wear additive may be metallic or non-metallic,
preferably the former.
Dihydrocarbyl dithiophosphate metal salts are examples of the anti-wear
additives. The metal in the dihydrocarbyl dithiophosphate may be an alkali or
alkaline earth metal, or aluminium, lead, tin, molybdenum, manganese, nickel
or
copper. Zinc salts are preferred, preferably in the range of 0.1 to 1.5,
preferably 0.5 to
1.3, mass %, based upon the total mass of the lubricating oil composition.
They may
be prepared in accordance with known techniques by firstly forming a
dihydrocarbyl
dithiophosphoric acid (DDPA), usually by reaction of one or more alcohols or a
phenol with F'2S5 and then neutralizing the formed DDPA with a zinc compound.
For
example, a dithiophosphoric acid may be made by reacting mixtures of primary
and
secondary alcohols. Alternatively, multiple dithiophosphoric acids can be
prepared
comprising both hydrocarbyl groups that are entirely secondary and hydrocarbyl
groups that are entirely primary. To make the zinc salt, any basic or neutral
zinc
compound may be used but the oxides, hydroxides and carbonates are most
generally
employed. Commercial additives frequently contain an excess of zinc due to use
of
an excess of the basic zinc compound in the neutralisation reaction.
The preferred zinc dihydrocarbyl dithiophosphates arc oil-soluble salts of
dihydrocarbyl dithiophosphoric acids and may be represented by the following
formula:
[(RU) (RIO) P(S)S]2 Zn
where R and RI may be the same or different hydrocarbyl radicals containing
from 1
to 18, preferably 2 to 12, carbon atoms and including radicals such as alkyl,
alkenyl,
aryl, arylalkyl, alkaryl and cycloaliphatic radicals. Particularly preferred
as R and RI
groups are alkyl groups of 2 to 8 carbon atoms. Thus, the radicals may, for
example,
be ethyl, n-propyl, I-propyl, n-butyl, 1-butyl, sec-butyl, amyl, n-hexyl, I-
hexyl, n-octyl,
decyl, dodecyl, octadecyl, 2-ethylehexyl, phenyl, butylphenyl, cyclohexyl,
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CA 02799383 2012-12-20
=
methylcyclopentyl, propenyl, butenyl. In order to obtain oil-solubility, the
total
number of carbon atoms (i.e. in R and R1) in the dithiophoshoric acid will
generally
be 5 or greater. The zinc dihydrocarbyl dithiophosphate can therefore comprise
zinc
dialkyl dithiophosphates.
If present, the anti-wear additive is preferably present in an amount from
0.10
to 3.0 mass %, based on the total amount of the lubricant composition.
Anti-oxidants
The trunk piston diesel engine lubricant composition may include at least one
anti-oxidant. The anti-oxidant may be aminic or phenolic. As examples of
amines
there may be mentioned secondary aromatic amines such as diarylamines, for
example diphenylamines wherein each phenyl group is alkyl-substituted with an
alkyl
group having 4 to 9 carbon atoms. As examples of anti-oxidants there may be
mentioned hindered phenols, including mono-phenols and bis-phenols.
Preferably, the anti-oxidant, if present, is provided in the composition in an
amount of up to 3 mass %, based on the total amount of the lubricant
composition.
Other additives such as pour point depressants, anti-foamants, metal rust
inhibitors, pour point depressants and/or demulsifiers may be provided, if
necessary.
The terms 'oil-soluble' or 'oil-dispersable' as used herein do not necessarily
indicate that the compounds or additives are soluble, dissolvable, miscible or
capable
of being suspended in the oil in all proportions. These do mean, however, that
they
are, for instance, soluble or stably dispersible in oil to an extent
sufficient to exert
their intended effect in the environment in which the oil is employed.
Moreover, the
additional incorporation of other additives may also permit incorporation of
higher
levels of a particular additive, if desired.
The lubricant compositions of this invention comprise defined individual (i.e.
separate) components that may or may not remain the same chemically before and
after mixing.
17
It may be desirable, although not essential, to prepare one or more additive
packages or concentrates comprising the additives, whereby the additives can
be
added simultaneously to the oil of lubricating viscosity to form the
lubricating oil
composition. Dissolution of the additive package(s) into the lubricating oil
may be
facilitated by solvents and by mixing accompanied with mild heating, but this
is not
essential. The additive package(s) will typically be formulated to contain the
additive(s) in proper amounts to provide the desired concentration, and/or to
carry out
the intended function in the final formulation when the additive package(s)
is/are
combined with a predetermined amount of base lubricant.
Thus, the additives 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 to 90, preferably from 5 to 75, most preferably from 8 to
60,
mass % of additives in the appropriate proportions, the remainder being base
oil.
The final formulations may typically contain about 5 to 40 mass % of the
additive packages(s), the remainder being base oil.
EXAMPLES
The present invention is illustrated by, but in no way limited to, the
following
examples.
Examples
The following examples use a centrifuge water shedding test which evaluates
the ability of an oil to shed water from a prepared test mixture of oil and
water. The
test uses an Alfa LavalTM MAB103B 2.0 centrifuge coupled to a Watson Marlow
peristaltic pump. The centrifuge is sealed with 2 litres of water. A
measurement is
made of the amount of deposits formed in the centrifuge during the test. The
test is
carried out at 87 C. Pre-measured amounts of water and the test oil are mixed
together and then passed through the centrifuge at a rate of 2 litres/min. The
test is
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CA 02799383 2012-12-20
=
run for an hour and a half, allowing the mixture to pass through the
centrifuge about
times. The centrifuge is weighed before and after the test. A poor trunk
piston
diesel engine lubricant composition will produce a larger amount of deposits
in the
centrifuge system.
Trunk piston engine oils ('IPEOs') were prepared having TBNs of about 40.
The TPEOs were subjected to the centrifuge water shedding test. Details of the
TPEOs and the test results are shown below in Table 1.
TABLE 1
Example Reference 1 2
Co-Additives 16 16 16
(mass %)
Lubricating Oil 75.5 82.3 80.94
(mass %)
Brightstock 8.5
(mass %)
PIB 2225 1.7
(mass %)
PIB 450 3.06
(mass %)
TBN 41.17 40.46 40.63
VI 104 105 104
Deposits (g)
Bowl 4 8 5
Hood 3 0 0
Top Disc 1 0 0
Distributor & Disc 37 4 28
Total Deposits (g) 45 12 33
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PIB = Polyisobutylene (number-average molelcular weight given).
The results show that Examples I and 2, containing PIB and no brightstock,
performed better in the water-shedding test than the Reference Example that
contained brightstock, but no PIB.
