Note: Descriptions are shown in the official language in which they were submitted.
CA 02471202 2011-01-13
Marine Diesel Cylinder Lubricant Composition
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, which
results in exhaust gases from diesel engines containing large amounts of
sulphur
oxides (SO,). 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).
There is growing environmental pressure to reduce the amount of sulphur in
fuels. Therefore, a marine diesel cylinder lubricant composition having a TBN
less than 70 could be used. However, the applicants have found that if a
marine
diesel cylinder lubricant composition is diluted with base oil to lower the
total
base number to less than 70, the ability of the lubricant to prevent deposit
formation, particularly on the pistons, is significantly reduced.
The aim of the present invention is to provide a marine diesel cylinder
lubricant
composition having a base number lower than 70 without reducing the ability of
the lubricant to prevent deposit formation, particularly on the pistons.
In accordance with the present invention there is provided a marine diesel
cylinder lubricant composition for a marine diesel engine running on fuel
having a
sulphur content of less than 1.5%, the composition having a total base number,
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as determined according to ASTM D2896, of more than 30 and less than 70, and
comprising:
- at least 40 wt% of an oil of lubricating viscosity, and
- at least one detergent prepared from at least two surfactants, one of
which is a salicylate.
The inventor has found that the marine diesel cylinder lubricant composition
defined above is capable of preventing deposit formation, particularly on the
pistons, and is also capable of improving resistance to high temperature-
induced
wear (i.e. scuffing).
The marine diesel cylinder lubricant composition has a total base number (TBN)
of less than 70, preferably less than 60, and most preferably less than 50.
Furthermore, the marine diesel cylinder lubricant composition preferably has a
total base number (TBN) of more than 32, more preferably more than 35.
In accordance with the present invention there is also provided a method of
operating a marine diesel cylinder engine running on fuel having at most 1.5%
sulphur, 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 deposits in a
marine diesel cylinder engine running on fuel having at most 1.5% sulphur.
In accordance with the present invention there is also provided use of the
marine
diesel cylinder lubricant composition defined above to provide lubricity in a
marine diesel cylinder engine running on fuel having at most 1.5% sulphur and
running at cylinder liner temperatures above 250 C, preferably above 300 C.
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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 1 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
typically have a kinematic viscosity at 1009C of from 2 to 40, for example
from 3
to 15, mm2s 1 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 10020 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.
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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.
Comolex/Hybrid Detergent
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.
The detergent is a complex/hybrid detergent including at least two
surfactants,
one of which is a salicylate. The complex detergent preferably includes at
least 5
mass% of salicylate, more preferably at least 10 mass% of salicylate. The
amount of salicylate 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 other surfactant may be a sulphonate, a
phenate,
a sulphurized phenate, a thiophosphate, a naphthenate, or an oil-soluble
carboxylate. The other surfactant is preferably a phenate. The complex
detergent preferably includes at least 5 mass% of phenate. The complex
detergent may also include at least 5 mass% of sulphonate. 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.
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Examples of complex detergents are described in WO 97/46645 and WO
97/46646.
Preferably, the detergent has a TBN in the range of 250 to 500, more
preferably
260 to 450.
Dispersants
The marine diesel cylinder lubricant composition may include at least one
dispersant. 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 succinimides, e.g. polyisobutene
succinic
anhydride; and polyamine condensation products that may be borated or
unborated.
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Anti-wear Additive
The marine diesel cylinder 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 metal 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 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 R1 may be the same or different hydrocarbyl radicals containing
from 1 to 18, preferably 2 to 12, carbon atoms and including radicals such as
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alkyl, alkenyl, aryl, arylalkyl, alkaryl and cycloaliphatic radicals.
Particularly
preferred as R and R1 groups are alkyl groups of 2 to 8 carbon atoms. Thus,
the
radicals may, for example, be ethyl, n-propyl, I-propyl, n-butyl, I-butyl, sec-
butyl,
amyl, n-hexyl, I-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 %.
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
A marine diesel cylinder lubricant composition was prepared using a commercial
additive package and commercial base oils. The lubricant composition had a
total base number of approximately 70 and comprised: an overbased complex
calcium detergent having a base number of 410 and including phenate and
sulphonate surfactants; a calcium phenate having a base number of 250; a
dispersant; and an anti-wear agent. It is noted that this marine diesel
cylinder
lubricant composition has been approved by marine diesel engine manufacturers
because it exhibits good performance in engine field tests. The lubricant was
subjected to the Panel Coker Test (details of which are shown below) for
piston
deposit control testing. The lubricant was then diluted to give a TBN of
approximately 40 and also tested using the Panel Coker Test. The test results
are shown below in Table 1:
Table 1
Comparative Example 1 Comparative Example 2
Total Base Number 74.1 43.6
Vk 100 18.7 17.0
Panel Coker Test
Results
Merit Rating 4.34 2.28
Deposits (mg) 34.1 50.7
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As shown in Table 1, when the marine diesel cylinder lubricant composition is
diluted to give a TBN of approximately 40, the merit rating and the amount of
deposits produced are worse.
Example 3 and Comparative Example 4 were then prepared (see Table 2 below)
and tested using the Panel Coker Test. Example 3 included a complex detergent
having a TBN of 350; the complex detergent included salicylate, phenate and
sulphonate surfactants. Example 4 included a complex detergent having a TBN
of 410; the complex detergent included phenate and sulphonate surfactants. It
is
noted that the complex detergent used in Comparative Example 4 is the same as
the complex detergent used in Comparative Example 1.
Table 2
Example 3 Comparative Example 4
Complex detergent 7.15
including salicylate,
sulphonate and phenate
surfactants
Complex detergent 6.10
including sulphonate and
phenate surfactants
Additive Package 8.60 8.60
comprising a 250
overbased calcium
phenate, a borated
dispersant, ZDDP and
Group I diluent base oil
Base Oil, APE 2500 20.00 20.00
available from
ExxonMobil
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Base Oil, APE 600 64.25 65.30
available from
ExxonMobil
Vk 100 17.2 16.8
BN 42.9 41.0
Panel Coker Test
Results
Merit Rating 5.06 2.46
Deposits (mg) 28.5 61.6
5
As shown above in Table 2, Example 3 has a base number of approximately 40
but it still exhibits good results in the Panel Coker Test. Furthermore, the
results
are better than those produced by Comparative Example 1, which has received
10 approval by the marine diesel engine manufacturers.
Comparative Example 4 shows that if the complex detergent does not include
any salicylate, the Panel Coker Test results are poor. Therefore, the complex
detergent including phenate and sulphonate as the surfactants is only suitable
for
use in marine diesel cylinder lubricant compositions having a TBN of at least
70.
The results in Table 2 clearly show that it is possible to formulate a marine
diesel
cylinder lubricant composition having a base number less than 70 without
adversely affecting the amount of deposits produced by the use of a complex
detergenf including salicylate as one of the surfactants.
The Panel Coker Test
This test involves splashing a lubricating oil composition on to a heated test
panel to see if the oil degrades and leaves any deposits that might affect
engine
performance. The test uses a panel coker tester (model PK-S) supplied by
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Yoshida Kagaku Kikal Co, Osaka, Japan. The test starts by heating the
lubricating oil composition to a temperature of 100 C through an oil bath. A
test
panel made of aluminium alloy, which has been cleaned using acetone and
heptane and weighed, is placed above the gas engine lubricating oil
composition
and heated to 320 C using an electric heating element. When both temperatures
have stabilised, a splasher splashes the gas engine lubricating oil
composition on
to the heated test panel in a discontinuous mode: the splasher splashes the
oil
for 15 seconds and then stops for 45 seconds. The discontinuous splashing
takes place over 1 hour, after which the test is stopped, everything is
allowed to
cool down, and then the aluminium test panel is weighed and rated visually.
The
difference in weight of the aluminium test panel before and after the test,
expressed in mg, is the weight of deposits. The visual rating is made from 0
to
10, with 0 being for a completely black panel and 10 being for a completely
clean
panel.
This test is used for simulating the ability of a lubricant composition to
prevent
deposit formation on pistons. Comparative Example 1 has been approved by
marine diesel engine manufacturers. Therefore, its performance in this test is
considered to be acceptable. A better lubricant composition would produce a
higher merit rating and a lower amount of deposits.
High Temperature HFRR Test
The HFRR Test, or High Frequency Reciprocating Rig Test, is a measure of in-
use lubricity and the test rig is described in CEC PF 06-T-94 or
ISO/TC22/SC7/WG6/N188. In these examples, the friction coefficient is
monitored at temperatures up to 350 C. When the friction coefficient reaches a
minimum, the temperature is recorded as the temperature of scuffing
initiation,
i.e. the temperature at which adhesive wear ('scuffing') begins.
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This test is used for assessing the ability of a lubricant composition to
control
adhesive wear in large bore crosshead engines. The result given for
Comparative Example 1 is considered to be acceptable by manufacturers of
marine diesel engines. A better lubricant composition would produce a higher
temperature of scuffing initiation.
Example 3 and Comparative Examples 1 and 2 were tested using the HFRR test.
The test results are shown below:
Table 3
Example 3 Comparative Comparative
Example 1 Example 2
Temperature of 338 270 277
Scuffing
Initiation
(degrees C)
As shown above, Example 3 provides `scuff-free' lubrication up to 338 C,
whereas Comparative Examples 1 and 2 only provide `scuff-free' lubrication up
to
270 C and 277 C respectively. These results show that marine diesel cylinder
lubricant compositions of the present invention having a total base number
below
70 can provide lubrication at higher temperatures than commercially available
lubricant compositions having total base numbers of at least 70.
