Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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MARINE DIESEL CYLINDER LUBRICANTS COMPRISING
COMPLEX DETERGENTS
This invention concerns a lubricant composition, in particular, a marine
diesel
cylinder lubricant (MDCL) composition. Marine diesel cylinder lubricant
compositions are total loss lubricants and their purpose is to provide a
strong oil
film between the cylinder liner and the piston rings and to neutralise acids
formed
by combustion of sulphur compounds in the fuel.
Fuels used for diesel engines generally have a high sulphur content (such as,
for
example, at least 3.5% sulphur), which results in exhaust gases from diesel
engines containing large amounts of sulphur oxides (SOX).. The sulphur oxides
react with moisture also present in the exhaust gases to form sulphuric acid
which corrodes the engine. Marine diesel cylinder lubricant compositions
therefore include overbased metallic detergents to neutralise the sulphuric
acid.
Commercial marine diesel cylinder lubricant compositions generally have
a,total
base number (`TBN') of at least 70 (as determined using ASTM D2896).
Environmental concerns have prompted many areas, such as coastal areas, to
require the use of low sulphur fuels, i.e. fuels including less than 1.00% by
weight
of sulphur, which allows the use of marine diesel cylinder lubricant
compositions
having lower total base numbers such as, for example, 40. This therefore
creates the need for ships to carry tanks for two different lubricants.
US 4,842,755 discloses a marine diesel cylinder lubricant having a base number
of at least 60. The composition includes a borated ashless dispersant, one or
more overbased metal compounds and a zinc dialkyl dithiophosphate providing
0.02 to 0.023 wt% (200-230 ppm) of zinc (see claim 1). The specific examples
show that increasing the amount of zinc above 230 ppm results in a loss in
performance benefits in ring and liner wear.
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An aim of the present invention is to provide a marine diesel cylinder
lubricant composition having a total base number of at least 30, preferably
at least 35, more preferably at least 40, and more preferably at least 60,
(ASTM D 2896-01), that is suitable for use with both high and low sulphur
fuels.
A further aim of the present invention is to provide a marine diesel cylinder
lubricant composition having a total base number of at least 30, preferably 35
or
more (ASTM D 2896-01), that is suitable for use with both high and low sulphur
fuels, whilst still providing the required level of protection against
corrosive wear
when used with a high sulphur fuel.
In accordance with the present invention there is provided a marine diesel
cylinder lubricant composition having a total base number, as determined
according to ASTM D2896, of at least 30, preferably at least 35 or more, and
comprising:
- at least 40 wt%, based on the total amount of the marine diesel
cylinder lubricant composition, of an oil of lubricating viscosity,
- at least one detergent prepared from at least two surfactants,
preferably phenate and sulphonate surfactants,
- at least one boron-containing dispersant providing at least 100 ppm of
boron, and
- at least one zinc-containing antiwear additive, preferably a zinc
dihydrocarbyl dithiophosphate, providing more than 230 ppm,
preferably at least 250 ppm, of zinc.
The inventors have surprisingly found, considering the teachings of US
4,842,755, that in a marine diesel cylinder lubricant composition including a
detergent prepared from at least two surfactants, the use of more than 230 ppm
zinc provides increased protection against wear.
The inventors have also found that the marine diesel cylinder lubricant
composition defined above provides a good level of wear protection even at a
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low total base number, such as, for example, 40, when used with a high sulphur
fuel.
In accordance with the present invention there is also provided a method of
operating a marine diesel engine, the method including the step of using the
marine diesel cylinder lubricant composition defined above to lubricate the
engine.
In accordance with the present invention there is also provided use of the
marine
diesel cylinder lubricant composition defined above to reduce wear in a marine
diesel engine.
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 marine engine. The lubricating oil
may
suitably be an animal, a 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 diesters such as di-octyl adipate, di-octyl sebacate and tridecyl
adipate, or polymeric hydrocarbon lubricating oils, for example liquid
polyisobutene and poly-alpha olefins. Commonly, a mineral oil is employed. The
lubricating oil may generally comprise greater than 60, typically greater than
70,
mass % of the composition, and typically have a kinematic viscosity at 100 C
of
from 2 to 40, for example for 3 to 15, mm2s'' and a viscosity index of from 80
to
100, for example from 90 to 95.
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
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typically have a 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
example from 105 to 108.
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 1 and are typically used in
a
proportion of less than 40, preferably less than 30, more preferably less than
20,
mass %, based on the mass of the composition.
The marine diesel cylinder lubricant composition preferably includes at least
50
wt% of oil of lubricating viscosity, more preferably at least 60 wt% of oil of
lubricating viscosity, even more preferably at least 70 wt% of oil of
lubricating
viscosity, based on the total amount of the marine diesel cylinder lubricant
' composition.
Deteraent including at least two Surfactants
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 based on metal "soaps", that is metal salts of acidic
organic
compounds, sometimes referred to as surfactants.
The 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.
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The detergent includes at least two surfactants, preferably at least phenate
and
sulphonate surfactants. The detergent may be referred to as a complex/hybrid
detergent. The complex detergent preferably includes at least 5 mass% of
phenate, more preferably at least 10 mass% of phenate, based on the total
5 amount of the detergent. The complex detergent preferably includes at least
5
mass% of sulphonate, more preferably at least 8 mass% of sulphonate, based on
the total amount of the detergent. The detergent preferably also includes a
salicylate surfactant. The detergent preferably includes at least 5 mass% of
salicylate, more preferably at least 10 mass% of salicylate, based on the
total
amount of the detergent. The amount of surfactant in the complex detergent can
be determined using techniques such as chromatography, spectroscopy and/or
titration, well known to persons skilled in the art. The detergent may also
include
other surfactants such as, for example, a thiophosphate, a naphthenate, or an
oil-soluble carboxylate. The surfactant groups are incorporated during the
overbasing process. The metal may be an alkali metal or an alkaline earth
metal
such as sodium, potassium, lithium, calcium and magnesium. Calcium is
preferred.
Examples of complex detergents are described in WO 97/46643, WO 97/46644,
WO 97/46645, WO 97/46646 and WO 97/46647.
Preferably, the detergent has a TBN in the range of 250 to 500, more
preferably
280 to 480, even more preferably 300 to 450.
The marine diesel cylinder lubricant composition preferably includes at least
2
wt%, preferably at least 5 wt%, more preferably at least 8 wt%, of detergent
including at least two surfactants, based on the total amount of the marine
diesel
cylinder lubricant composition.
The marine diesel cylinder lubricant may also include further detergents such
as
a calcium phenate detergent, a calcium sulphonate detergent or a calcium
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salicylate detergent. The further detergent may have a low TBN of less than
50,
a medium TBN ranging from 50 to 150 or a high TBN of more than 150. The
marine diesel cylinder lubricant composition preferably includes at least 4
wt%,
preferably at least 6 wt%, of a further detergent, based on the total amount
of the
marine diesel cylinder lubricant composition.
Disaersant
The marine diesel cylinder lubricant composition includes at least one
dispersant
providing at least 100 ppm of boron. A dispersant is an additive for a
lubricating
composition whose primary function in cylinder lubricants is to accelerate
neutralization of acids by the detergent system.
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 oleophilic 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 borated succinimides, e.g. borated
polyisobutene succinic anhydride; and polyamine condensation products that are
borated.
The marine diesel cylinder lubricant composition preferably includes at least
150
ppm, more preferably at least 200 ppm, of boron, based on the total amount of
the marine diesel cylinder lubricant composition.
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Antiwear Additive
The antiwear additive provides at least 230 ppm, preferably at least 250 ppm,
of
zinc, based on the total amount of the marine diesel cylinder lubricant
composition. The antiwear additive preferably provides at least 275 ppm, more
preferably at least 300 ppm, even more preferably at least 325 ppm, even more
preferably at least 350 ppm, even more preferably at least 375ppm and most
preferably at least 385 ppm, of zinc.
The antiwear additive 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 P2S5 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 are oil-soluble salts of
dihydrocarbyl dithiophosphoric acids and may be represented by the following
formula:
[(RO) (R'O) P(S)S]2 Zn
where R and R' 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 R' groups are alkyl groups of 2 to 8 carbon atoms. Thus,
the
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radicals may, for example, be ethyl, n-propyl, I-propyl, n-butyl, I-butyl, sec-
butyl,
amyl, n-hexyl, 1-hexyl, n-octyl, decyl, dodecyl, octadecyl, 2-ethylehexyl,
phenyl,
butylphenyl, cyclohexyl, methylcyclopentyl, propenyl, butenyl. In order to
obtain
oil-solubility, the total number of carbon atoms (i.e. in R and R) in the
dithiophoshoric acid will generally be 5 or greater. The zinc dihydrocarbyl
dithiophosphate can therefore comprise zinc dialkyl dithiophosphates.
Anti-oxidants
The marine diesel cylinder 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 marine diesel
cylinder lubricant.
Other additives such as pour point depressants, anti-foamants, 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.
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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.
The present invention is illustrated by, but in no way limited to, the
following
examples.
Examples
Marine diesel.cylinder lubricant compositions were prepared having TBNs of
either 40 or 70: The lubricant compositions comprised: an overbased complex
calcium detergent including phenate and sulphonate surfactants; a calcium
phenate having a base number of 250; a borated dispersant; and an anti-wear
agent.
TM
The lubricant compositions were subjected. to the Bolnes Test using a Bolnes
crosshead engine (a single cylinder 2-stroke engine, the Bolnes 3DNL),
calibrated and stabilized, operating on a fuel including about 3.5% sulphur.
The
Bolnes engine speed was 500 rpm with a lubricant feed rate of 1.00 gtkwh. Each
lubricant composition was tested for 96 hours. The test conditions were
designed to create corrosive wear of the cylinder liner over this time. Wear
was
measured in microns in specific calibrated places on the cylinder liner. The
average recorded wear is reported below. The lower the recorded result, the
less wear of the cylinder liner.
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Comparative Example 2 Example 3 Example 4 Example 5
Example 1
Detergent 15.24 12.10 10.80
including at
least two
surfactants
Detergent 14.30 7.15
including at
least two
surfactants
250 TBN 3.34 8.00 10.00 8.02 6.00
Calcium
Phenate
Detergent
Borated 3.05 3.00
Dispersant
Borated 3.00 2.67 2.00
Dispersant
Antiwear 0.28 1.00 0.50 0.67 0.50
Agent
Antioxidant 0.50
Base oils 78.09 75.90 75.20 74.34 84.35
Base Number 70 70 70 70 40
(ASTM D
2896-01)
Boron (ppm) 107 105 390 347 260
Zinc (ppm) 216 770 385 516 385
Bolnes Test
Liner Wear, 19 10 11 12 12
average
The above table clearly shows that less wear is produced with marine diesel
5 cylinder lubricants including 385 ppm or more of zinc when the detergent is
prepared from at least two surfactants. It is particularly surprising that
example
5, which has a TBN of 40, produces less wear with the high sulphur fuel than
comparative example 1 which has a TBN of 70.
