Note: Descriptions are shown in the official language in which they were submitted.
CA 02856378 2014-07-09
MARINE ENGINE LUBRICATION
FIELD OF THE INVENTION
This invention relates to a method for improving asphaltene dispersancy in a
trunk
piston marine engine.
This invention also relates to use of a detergent system for improving
asphaltene
dispersancy in a trunk piston marine engine.
This invention also relates to the use of a detergent system comprising a
combination
of hydroxybenzoates in a trunk piston marine engine lubricating composition
for a medium-
speed four-stroke compression-ignited (diesel) marine engine to improve the
asphaltene
dispersancy performance of the composition.
BACKGROUND OF THE INVENTION
Marine trunk piston engines generally use Heavy Fuel Oil (HF0') for offshore
running. Heavy Fuel Oil is the heaviest fraction of petroleum distillate and
comprises a
complex mixture of molecules including up to 15% of asphaltenes, defined as
the fraction of
petroleum distillate that is insoluble in an excess of aliphatic hydrocarbon
(e.g. heptane) but
that is soluble in aromatic solvents (e.g. toluene). Asphaltenes can enter the
engine lubricant
as contaminants either via the cylinder or the fuel pumps and injectors, and
asphaltene
precipitation can then occur, manifested in 'black paint' or 'black sludge' in
the engine. The
presence of such carbonaceous deposits on a piston surface can act as an
insulating layer
which can result in the formation of cracks that then propagate through the
piston If a crack
travels through the piston, hot combustion gases can enter the crankcase,
possibly resulting in
a crankcase explosion.
It is therefore highly desirable that trunk piston engine oils (`TPEO's)
prevent or
inhibit asphaltene precipitation.
EP-B-1992 678 describes trunk piston engine oils that contain combinations of
overbased alkylsalicylic acid calcium salts for improving wear properties. No
mention is
made of asphaltene dispersancy.
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It is now found that, by using certain hydroxybenzoate combinations in a TPEO,
it is
possible to achieve improved asphaltene dispersancy properties.
SUMMARY OF THE INVENTION
A first aspect of the invention is a method for improving asphaltene
dispersancy in a
trunk piston marine engine, the method comprising lubricating the engine with
a lubricating
oil composition comprising a detergent system that includes (i) an overbased
alkyl-substituted
hydroxybenzoate calcium salt of TBN less than 250, which alkyl group has 20-28
carbon
atoms, and (ii) an overbased alkyl-substituted hydroxybenzoate calcium salt of
TBN less than
250, which alkyl group has 14-18 carbon atoms; the wt% Ca ratio of (ii) to (i)
being greater
than one.
A second aspect of the invention is the use of a detergent system that
includes (i) an
overbased alkyl-substituted hydroxybenzoate calcium salt of TBN less than 250.
which alkyl
group has 20-28 carbon atoms, in a trunk piston marine lubricating oil
composition for a
medium-speed compression-ignited marine engine during operation of the engine,
where the
detergent system further comprises (ii) an overbased alkyl-substituted
hydroxybenzoate
calcium salt of TBN less than 250, which alkyl group has 14-18 carbon atoms,
the wt% Ca
ratio of (ii) to (i) being greater than one, said use being to improve the
asphaltene dispersancy
performance of the composition.
A third aspect of the invention is the use of a detergent system that includes
(i) an
overbased alkyl-substituted hydroxybenzoate calcium salt of TBN less than 250,
which alkyl
group has 20-28 carbon atoms, in a trunk piston marine lubricating oil
composition for a
medium-speed compression-ignited marine engine during operation of the engine,
fueled by a
heavy fuel oil, and its lubrication by the composition, where the detergent
system further
comprises (ii) an overbased alkyl-substituted hydroxybenzoate calcium salt of
TBN less than
250, which alkyl group has 14-18 carbon atoms, the wt% Ca ratio of (ii) to (i)
being greater
than one, said use being to improve the asphaltene dispersancy performance of
the
composition in comparison with that of analogous operation using a detergent
system whose
wt% Ca ratio is one or less and/or where (ii) has a TBN of 250 or greater.
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In this specification, the following words and expressions, if and when used,
have the
meanings ascribed below:
"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, preferably 40 mass %
or
more of a composition, more preferably 30 mass % or more of a composition;
"minor amount" means less than 50 mass % of a composition, preferably less
than 40
mass % of a composition, more preferably less than 30 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.
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.
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OIL OF LUBRICATING VISCOSITY
The trunk piston marine lubricating oil composition of the invention comprises
a
major amount of an oil of lubricating viscosity. That may range in viscosity
from light
distillate mineral oils to heavy lubricating oils. Such oil may be referred to
as base oil.
Generally, the viscosity of the oil ranges from 2 to 40 mm2/sec, as measured
at 100 C. The oil
may be a natural or a synthetic oil.
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 may also be used.
Synthetic lubricating oils include hydrocarbon oils and halo-substituted
hydrocarbon
oils such as polymerized and interpolymerized olefins (e.g., polybutylenes,
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 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 may be 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 C13 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
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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 sebacate,
the 2-ethylhexyl
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 such as neopentyl glycol, trimethylolpropane,
pentaerythritol,
dipentaerythritol and tripentaerythritol.
Silicon-based oils such as polyalkyl-, polyaryl-, polyalkoxy- or
polyaryloxysilicone
oils and silicate oils comprise another useful class of synthetic oils; such
oils include
tetraethyl silicate, tetraisopropyl silicate, tetra-(2-ethylhexyl)silicate,
tetra-(4-methy1-2-
ethylhexyl)silicate, tetra-(p-tert-butyl-phenyl)
silicate, hexa-(4-methy1-2-
ethylhexyl)disiloxane, poly(methypsiloxanes and 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. Refined
oils are similar to unrefined oils except that the oil is further treated in
one or more
purification steps to improve one or more properties. Many such purification
techniques, such
as distillation, solvent extraction, acid or base extraction, filtration and
percolation, are known
to those skilled in the art. Re-refined oils are obtained by processes similar
to those used to
provide refined oils but begin with oil that has already been used in service.
Such re-refined
oils are also known as reclaimed or reprocessed oils and are often subjected
to additional
processing using techniques for removing spent additives and oil breakdown
products.
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The American Petroleum Institute (API) publication "Engine Oil Licensing and
Certification System", Industry Services Department, Fourteenth Edition,
December 1996,
Addendum 1, December 1998 categorizes base stocks as follows:
a) Group I base stocks contain less than 90 percent saturates and/or greater
than 0.03
percent sulphur and have a viscosity index greater than or equal to 80 and
less than 120
using the test methods specified in Table E-1.
b) Group II base stocks contain greater than or equal to 90 percent saturates
and less
than or equal to 0.03 percent sulphur and have a viscosity index greater than
or equal to
80 and less than 120 using the test methods specified in Table E-1.
c) Group III base stocks contain greater than or equal to 90 percent saturates
and less
than or equal to 0.03 percent sulphur and have a viscosity index greater than
or equal to
120 using the test methods specified in Table E-1.
d) Group IV base stocks are polyalphaolefins (PAO).
e) Group V base stocks include all other base stocks not included in Group I,
11, III, or
IV.
Analytical Methods for Base Stock are tabulated below (Table E-1):
PROPERTY TEST METHOD
Saturates ASTM D 2007
Viscosity Index ASTM D 2270
Sulphur ASTM D 2622
ASTM D 4294
ASTM D 4927
ASTM D 3120
By way of example, the present invention embraces Group II, Group III and
Group IV
basestocks and also basestocks derived from hydrocarbons synthesised by the
Fischer-
Tropsch process. In the Fischer-Tropsch process, synthesis gas containing
carbon monoxide
and hydrogen (or `syngas') is first generated and then converted to
hydrocarbons using a
Fischer-Tropsch catalyst. These hydrocarbons typically require further
processing in order to
be useful as a base oil. For example, they may, by methods known in the art,
be
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hydroisomerized; hydrocracked and hydroisomerized; dewaxed; or hydroisomerized
and
dewaxed. The syngas may, for example, be made from gas such as natural gas or
other
gaseous hydrocarbons by steam reforming, when the resulting basestock may be
referred to as
gas-to-liquid ("GTL") base oil; or from gasification of biomass, when the
resulting basestock
may be referred to as biomass-to-liquid ("BTL" or "BMTL") base oil; or from
gasification of
coal, when the resulting basestock may be referred to as coal-to-liquid ("CTL-
) base oil.
Preferably, the oil of lubricating viscosity in this invention contains 50
mass % or
more of a basestock containing 50 mass % or more of a basestock containing
greater than or
equal to 90 % saturates and less than or equal to 0.03 % sulphur or a mixture
thereof
Preferably, it contains 60, such as 70, 80 or 90, mass % or more of the
defined basestock or a
mixture thereof. The oil of lubricating viscosity may be substantially all of
the defined
basestock or a mixture thereof.
Most preferably, the oil of lubricating viscosity in this invention contains
50 mass %
or more of a basestock containing 50 mass % or more of a basestock containing
less than 90%
saturates and greater than 0.03 % sulphur or a mixture thereof. Preferably, it
contains 60,
such as 70, 80 or 90, mass % or more of the defined basestock or a mixture
thereof The oil
of lubricating viscosity may be substantially all of the defined basestock or
a mixture thereof.
The composition may have a TBN in the range of 20-60, preferably 25-55.
DETERGENT SYSTEM
A metal detergent is an additive based on so-called metal "soaps", that is
metal salts of
acidic organic compounds, sometimes referred to as surfactants. They generally
comprise a
polar head with a long hydrophobic tail. Overbased metal detergents, which
comprise
neutralized metal detergents as the outer layer of a metal base (e.g.
carbonate) micelle, may be
provided by including large amounts of metal base by reacting an excess of a
metal base, such
as an oxide or hydroxide, with an acidic gas such as carbon dioxide.
In the present invention, detergents (i) and (ii) of the invention are
overbased alkyl-
substituted hydroxybenzoate calcium salts, preferably alkyl-substituted
salicylate calcium
salts.
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A salicylate detergent of such a system typically has the structure shown:
/ OH
¨C Ca2'
R
\Oi
wherein R is a linear alkyl group. There may be more than one R group attached
to the
benzene ring. The C00- group can be in the ortho, meta or para position with
respect to the
hydroxyl group; the ortho position is preferred. The R group can be in the
ortho, meta or para
position with respect to the hydroxyl group.
In (i), R has 20-28, preferably 20-24, carbon atoms. In (ii), R has 14-18
carbon
atoms. Each of (i) and (ii) may be mixtures.
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.
Salicylic acids may be non-sulphurized or
sulphurized, and may be chemically modified and/or contain additional
substituents.
Processes for sulphurizing an alkyl salicylic acid are well known to those
skilled in the art and
are described, for example, in US 2007/0027057.
The term "overbased" is generally used to describe metal detergents in which
the ratio
of the number of equivalents of the metal moiety to the number of equivalents
of the acid
moiety is greater than one. The term 'low-based' is used to describe metal
detergents in
which the equivalent ratio of metal moiety to acid moiety is greater than 1,
and up to about 2.
The basicity of the detergents may be expressed as a total base number (TBN).
A total
base number is the amount of acid needed to neutralize all of the basicity of
the overbased
material. The TBN may be measured using ASTM standard D2896 or an equivalent
procedure. The detergents, as stated, each have a TBN of below 250; for
example the TBN is
in the range of 60 to 250, preferably 150 to 250.
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The wt % Ca ratio of (ii) to (i) is as stated greater than one, for example in
the range of
1 to 50, preferably 1 to 3.
The treat rate of the detergent system contained in the lubricating oil
composition may
for example be in the range of 1 to 25, preferably 2 to 20, more preferably 5
to 18, mass %.
CO-ADDITIVES
The lubricating oil composition of the invention may comprise further
additives,
different from and additional to the detergent system. Such additional
additives may, for
example include ashless dispersants, other metal detergents, anti-wear agents
such as zinc
dihydrocarbyl dithiophosphates, anti-oxidants and demulsifiers. In some cases,
an ashless
dispersant need not be provided.
It may be desirable, although not essential, to prepare one or more additive
packages
or concentrates comprising the additives, whereby the detergent system can be
added
simultaneously to the base oil 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 oil.
Thus, the
detergent system, 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 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 as a trunk piston engine oil may typically contain 30,
preferably 10 to 28, more preferably 12 to 24, mass ')/0 of the additive
package(s), the
remainder being base oil.
The present invention is illustrated by but in no way limited to the following
examples.
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411*,
A
EXAMPLES
COMPONENTS
The following components were used:
Detergent (ii):
A: a calcium alkylsalicylate detergent of TBN 225 and whose alkyl
group
has 14-18 carbon atoms.
B: a calcium alkylsalicylate detergent of TBN 350 whose alkyl group has
14-18 carbon atoms.
C: a calcium alkylsalicylate detergent of "1BN 64 and whose alkyl group
has 14-18 carbon atoms.
Detergent (i): a calcium alkylsalicylate detergent of TBN 223
whose alkyl group has
20-24 carbon atoms
Base oil I: solvent-extracted API Group I base oil
HFO: a heavy fuel oil (ISO-F-RMK 380)
LUBRICANTS
Selections of the above components were blended to give a range of trunk
piston
marine engine lubricants. Some of the lubricants are examples of the
invention; others are
reference examples for comparison purposes. The compositions of the lubricants
tested are
shown in the tables below under the "Results" heading. Each lubricant had a
TBN of about 40.
Each lubricant also contained the same amount of HFO.
TESTING
Light Scattering
Test lubricants were evaluated for asphaltene dispersancy using light
scattering
according to the Focused Beam Reflectance Method ("FBRM"), which predicts
asphaltene
agglomeration and hence 'black sludge' formation.
The FBRM test method was disclosed at the 7th International Symposium on
Marine
Engineering, Tokyo, 24th - 28th October 2005, and was published in 'The
Benefits of
Salicylate Detergents in TPEO Applications with a Variety of Base Stocks', in
the Conference
Proceedings. Further details were disclosed at the CIMAC Congress, Vienna,
21st -24th May
2007 and published in "Meeting the Challenge of New Base Fluids for the
Lubrication of
Medium Speed Marine Engines ¨ An Additive Approach" in the Congress
Proceedings. In
the latter paper it is disclosed that by using the FBRM method it is possible
to obtain
quantitative results for asphaltene dispersancy that predict performance for
lubricant systems
based on base stocks containing greater than or less than 90% saturates, and
greater than or
less than 0.03% sulphur. The predictions of relative performance obtained from
FBRM were
confirmed by engine tests in marine diesel engines.
The FBRM probe contains fibre optic cables through which laser light travels
to reach
the probe tip. At the tip, an optic focuses the laser light to a small spot.
The optic is rotated
so that the focussed beam scans a circular path between the window of the
probe and the
sample. As particles flow past the window, they intersect the scanning path,
giving
backscattered light from the individual particles.
The scanning laser beam travels much faster than the particles; this means
that the
particles are effectively stationary. As the focussed beam reaches one edge of
the particle the
amount of backscattered light increases; the amount will decrease when the
focussed beam
reaches the other edge of the particle.
The instrument measures the time of the increased backscatter. The time period
of
backscatter from one particle is multiplied by the scan speed and the result
is a distance or
chord length. A chord length is a straight line between any two points on the
edge of a
particle. This is represented as a chord length distribution, a graph of
numbers of chord
lengths (particles) measured as a function of the chord length dimensions in
microns. As the
measurements are performed in real time, the statistics of a distribution can
be calculated and
tracked. FBRM typically measures tens of thousands of chords per second,
resulting in a
robust number-by-chord length distribution. The method gives an absolute
measure of the
particle size distribution of the asphaltene particles.
TM
The Focused beam Reflectance Probe (FBRM), model Lasentec D600L, was supplied
by Mettler Toledo, Leicester, UK. The instrument was used in a configuration
to give a
particle size resolution of 1 lam to 1mm. Data from FBRM can be presented in
several ways.
Studies have suggested that the average counts per second can be used as a
quantitative
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CA 02856378 2014-07-09
determination of asphaltene dispersancy. This value is a function of both the
average size and
level of agglomerate. In this application, the average count rate (over the
entire size range)
was monitored using a measurement time of 1 second per sample.
The test lubricant formulations were heated to 60 C and stirred at 400rpm;
when the
temperature reached 60 C the FBRM probe was inserted into the sample. An
aliquot of heavy
fuel oil (10% w/w) was introduced into the lubricant formulation under
stirring using a four-
blade stirrer (at 400 rpm). A value for the average counts per second was
taken when the
count rate had reached an equilibrium value (typically after 30 minutes).
RESULTS
Light Scattering
The results of the FBRM tests are summarized in TABLE 1 below, where lower
particle count indicates better performance.
Example 1 is an example of the invention and Examples A-F are comparison
examples.
RESULTS
Example C14-18 alkyl C14-18 alkyl C14-18 alkyl C20-24 alkyl
Ca ratio Lasentec
salicylate salicylate salicylate salicylate (ii)
to (i) Count
(225) (ii) (350) (ii) (64) (ii) (223) (i)
A
1 10.00 7.90 1.28 40.1
A 8.40 = 5.00 2.65 377.7
6.00 8.50 1.11 333.8
3.00 13.00 0.36 700.2
17.94 243.4
5.00 8.30 1037.6
9.80 10.00 187.8
Numbers in parentheses after the salicylate are TBN's.
As shown above, the lowest Lasentec count is achieved by the use of Example 1
which falls within the invention. (Lower particle count indicates better
performance.)
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