Note: Descriptions are shown in the official language in which they were submitted.
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ADDITIVES AND FUEL OIL COMPOSITIONS
This invention relates to additives for improving the lubricity of fuel oils
such as
diesel fuel oil. Diesel fuel oil compositions including the additives exhibit
improved
lubricity and reduced engine wear.
Concem for the environment has resulted in moves to significantly reduce the
noxious components in emissions when fuel oils are bumt, particularly in
engines such as
diesel engines. Attempts are being made, for example, to minimise sulphur
dioxide
emissions. As a consequence attempts are being made to minimise the sulphur
content
of fuel oils. For example, although typical diesel fuel oils have in the past
contained 1%
by weight or more of sulphur (expressed as elemental sulphur) it is now
considered
desirable to reduce the level, preferably to 0.05% by weight and,
advantageously, to less
than 0.01 % by weight, particularly less than 0.001 % by weight.
Additional refining of fuel oils, necessary to achieve these low sulphur
levels, often
results in reductions in the level of polar components. In addition, refinery
processes can
reduce the level of polynuclear aromatic compounds present in such fuel oils.
Reducing the level of one or more of the sulphur, polynuclear aromatic or
polar
components of diesel fuel oil can reduce the ability of the oil to lubricate
the injection
system of the engine so that, for example, the fuel injection pump of the
engine fails
relatively early in the life of an engine. Failure may occur in fuel injection
systems such as
high pressure rotary distributors, in-line pumps and injectors. The problem of
poor
lubricity in diesel fuel oils is likely to be exacerbated by the future engine
developments
aimed at further reducing emissions, which will have more exacting lubricity
requirements
than present engines. For example, the advent of high pressure unit injectors
is
anticipated to increase the fuel oil lubricity requirement.
Similarly, poor lubricity can lead to wear problems in other mechanical
devices
dependent for lubrication on the natural lubricity of fuel oil.
Lubricity additives for fuel oils have been described in the art. WO 94/17160
describes an additive which comprises an ester of a carboxylic acid and an
alcohol
wherein the acid has from 2 to 50 carbon atoms and the alcohol has one or more
carbon
atoms. Glycerol monooleate is specifically disclosed as an example. Although
general
mixtures are contemplated, no specific mixtures of esters are disclosed.
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US-A-3,273,981 discloses a lubricity additive being a mixture of A+B wherein A
is
a polybasic acid, or a polybasic acid ester made by reacting the acid with C1-
C5
monohydric alcohols; while B is a partial ester of a polyhydric alcohol and a
fatty acid, for
example glyceryl monooleate, sorbitan monooleate or pentaerythritol
monooleate. The
mixture finds application in jet fuels.
However, in certain circumstances such prior art esters have unexpectedly been
found to promote the blocking of fuel filters, particularly the fine-mesh
filters typically
present in diesel vehicle fuel lines. This filter-blocking problem can result
in insufficient
fuel flow and impaired engine operation, and is especially apparent at low
temperatures.
Furthermore, it has unexpectedly been found that fuels containing the
preferred
ester (Additive D) described in WO 94/17160 shows a loss of lubricity
performance
following a period of cold storage and filtration. The loss of performance can
be apparent
even in the absence of severe filter blocking problems. This loss in
performance itself
represents a significant problem, because under field conditions a stored fuel
oil is
typically subjected to temperature cycles and must still be able to impart
effective
lubrication to mechanical devices downstream of the fuel-line filters. In a
diesel vehicle
fuel system, for example, diesel fuel must first flow through a fine-grade
filter before
reaching the fuel injection system, including the injection pump. Decreased
lubricity
performance after this filtration point therefore exposes the injection system
to increased
wear.
There thus exists a need for improved lubricity additives which demonstrate
better
filterability and which, in fuel oils, do not show a loss in performance after
filtration
following periods of cold temperature storage.
Such problems have now surprisingly been solved by additives which comprise
specific mixtures of certain esters.
GB-A-1,505,302 describes ester combinations including, for example, glycerol
monoesters and glycerol diesters as diesel fuel additives, the combinations
being
described as leading to advantages including less wear of the fuel-injection
equipment,
piston rings and cylinder liners. GB-i4-1,505,302 is, however, concemed with
overcoming
the operational disadvantages of corrosion and wear by acidic combustion
products,
residues in the combustion chamber and in the exhaust system. The document
states
that these disadvantages are due to incomplete combustion under certain
operating
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conditions. Typical diesel fuels available at the date of the document
contained, for
example, from 0.5 to 1% by weight of sulphur, as elemental sulphur, based on
the weight
= of the fuel.
US-A-3,287,273 describes lubricity additives which are reaction products of a
dicarboxylic acid and an oil-insoluble glycol. The acid is typically
predominantly a dimer of
unsaturated fatty acids such as linoleic or oleic acid, although minor
proportions of the
monomer acid may also be present. Only alkane diols or oxa-alkane diols are
specifically
suggested as the glycol reactant.
In a first aspect therefore, the invention provides a fuel oil composition
comprising
a major proportion of a middle distillate fuel oil having a sulphur content of
0.2% by weight
or less, and a minor proportion of a lubricity additive comprising:
(a) an ester of an unsaturated monocarboxylic acid and a polyhydric alcohol,
and
(b) an ester of an unsaturated monocarboxylic acid and a polyhydric alcohol
having at least three hydroxy groups,
the esters (a) and (b) being different.
In a second aspect, the invention provides the use of the additive defined in
the
first aspect, for improving the lubricity of a middle distillate fuel oil.
In a third aspect, the invention provides the use of the fuel composition of
the first
aspect in a combustion apparatus for reducing the wear rate in the fuel supply
system of
said apparatus.
Another embodiment of this invention is a method for reducing the wear rate in
the
fuel supply system of a combustion apparatus which employs a middle distillate
fuel oil
= having a sulfur content of 0.2% by weight or less, which comprises adding to
said fuel in
an amount effective to reduce the wear rate, a minor proportion of a lubricity
additive
comprising a blend of two different esters prepared respectively from an
unsaturated
monocarboxylic acid and a polyhydric alcohol, and an unsaturated
monocarboxylic acid
and a polyhydric alcohol which has at least three hydroxy groups.
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The mixture of esters (a) and (b) can provide unexpectedly improved lubricity
performance when compared to the individual performance of component (a) or
(b).
Furthermore, the mixture of (a) and (b) shows improved filterability and
maintains good
lubricity performance after cold storage followed by filtration.
The invention will now be described in more detail.
The Fuel Oil Composition (first aspect of the invention)
(i) The Additive
The term 'polyhydric alcohol' is used to describe a compound having more than
one hydroxy-group. It is preferred that (a) is the ester of a polyhydric
alcohol having at
least three hydroxy groups.
Examples of polyhydric alcohols having at least three hydroxy groups are those
having 3 to 10, preferably 3 to 6, more preferably 3 to 4 hydroxy groups and
having 2 to
90, preferably 2 to 30, more preferably 2 to 12 and most preferably 3 to 4
carbon atoms in
the molecule. Such alcohols may be aliphatic, saturated or unsaturated, and
straight
chain or branched, or cyclic derivatives thereof. Saturated, aliphatic,
straight chain
alcohols are preferred.
Advantageously, both (a) and (b) are esters of trihydric alcohols, especially
glycerol or trimethylol propane. Other suitable polyhydric alcohols include
pentaerythritol,
sorbitol, mannitol, inositol, glucose and fructose.
The unsaturated monocarboxylic acids from which the esters are derived may
have an alkenyl, cyclo alkenyl or aromatic hydrocarbyl group attached to the
carboxylic
acid group. The term 'hydrocarbyl' means a group containing carbon and
hydrogen which
may be straight chain or branched and which is attached to the carboxylic acid
group by a
carbon-carbon bond. The hydrocarbyl group may be interrupted by one or more
hetero '
atoms such as 0, S, N or P.
It is preferred that (a) and (b) are both esters of alkenyl monocarboxylic
acids, the
alkenyl groups preferably having 10 to 36, for example 10 to 22, more
preferably 18-22,
especially 18 to 20 carbon atoms. The alkenyl group may be mono- or poly-
unsaturated.
It is particularly preferred that (a) is an ester of a mono-unsaturated
alkenyl
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monocarboxylic acid, and that (b) is an ester of a poly-unsaturated alkenyl
monocarboxylic acid. The poly-unsaturated acid is preferably di- or tri-
unsaturated.
Such acids may be derived from natural materials, for example vegetable or
animal
extracts.
Especially-preferred mono-unsaturated acids are oleic and elaidic acid.
Especially
preferred poly-unsaturated acids are linoleic and linolenic acid.
It has been found that the mixtures wherein (a) is an ester of a mono-
unsaturated
acid and (b) is an ester of a poly-unsaturated acid have especially good
lubricity
performance and exhibit particularly good filterability and resistance to cold
storage.
The esters may be partial or complete esters, i.e. some or all of the hydroxy
groups of each polyhydric alcohol may be esterified. It is preferred that at
least one of (a)
or (b) is a partial ester, particularly a monoester. Especially good
performance is obtained
where (a) and (b) are both partial esters and particularly where both are
monoesters.
The esters may be prepared by methods well known in the art, for example by
condensation reactions. If desired, the alcohols may be reacted with acid
derivatives
such as anhydrides or acyl chlorides in order to facilitate the reaction and
improve yields.
The esters (a) and (b) may be separately prepared and then mixed together, the
mixing occuring either prior to addition to the fuel, or as a result of
separate addition of (a)
and (b) to the fuel at the same or different times. Altematively, the ester
mixture may be
prepared directly from a mixture of appropriate starting materials. It has
been found that
the latter products (i.e. those ester mixtures formed directly from the
reaction of a mixture
of starting materials) have particularly good filterability and show
especially good lubricity
performance. In particular, commercially-available mixtures of suitable acids
may be
reacted with a selected alcohol such as glycerol to form a mixed ester product
according
to this invention. Particularly-preferred commercial acid mixtures are those
comprising
oleic and linoleic acids. In such mixtures, a minor proportion of other acids,
or acid
= polymerisation products, may be present but this proportion preferably
should not exceed
15%, more preferably not more than 10%, and most preferably not more than 5%
by
weight of the total acid mixture.
Similarly, mixtures of esters may be prepared by reacting a single acid with a
mixture of alcohols.
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A highly-preferred ester mixture is that obtained by reacting a mixture of
oleic and
linoleic acids with glycerol, the mixture comprising predominantly (a)
glycerol monooleate
and (b) glycerol monolinoleate, preferably in approximately equal proportions
by weight.
In addition to the esters (a) and (b), the lubricity additive may further
comprise a =
minor proportion of other esters formed, for example, during esterification of
the acid
mixtures previously described.
(ii) The Fuel Oil
The fuel oil may be a petroleum-based fuel oil, suitably a middle distillate
fuel oil,
i.e. a fuel oil obtained in refining crude oil as the fraction between the
lighter kerosene and
jet fuels fraction and the heavy fuel oil fraction. Such distillate fuel oils
generally boil
above about 100 C. The fuel oil can comprise atmospheric distillate or vacuum
distillate,
or cracked gas oil or a blend in any proportion of straight run and thermally
and/or
catalytically cracked distillates. The most common petroleum-based fuel oils
are
kerosene, jet fuels and preferably diesel fuel oils.
The sulphur content of the fuel oil is 0.2% by weight or less, preferably
0.05% by
weight or less, more preferably 0.01 % by weight or less, and most preferably
0.001 % by
weight or less based on the weight of the fuel oil. The art describes methods
for reducing
the sulphur content of hydrocarbon middle distillate fuels, such methods
including solvent
extraction, sulphuric acid treatment, and hydrodesulphurisation.
Preferred fuel oils have a cetane number of at least 40, preferably above 45
and
more preferably above 50. The fuel oil may have such cetane numbers prior to
the
addition of any cetane improver or the cetane number of the fuel may be raised
by the
addition of a cetane improver.
More preferably, the cetane number of the fuel oil is at least 52.
(iii) Treat Rates
The concentration of the additive in the fuel oil may for example be in the
range of
10 to 5,000 ppm of additive (active ingredient) by weight per weight of fuel
oil, for example
20 to 5,000 ppm such as 50 to 2000 ppm (active ingredient) by weight per
weight of fuel,
preferably 75 to 300 ppm, more preferably 100 to 200 ppm.
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The relative proportions of (a) and (b) by weight within the fuel oil may be
in the
range of 1:10 to 10:1, preferably 1:4 to 4:1 and more preferably 1:2 to 2:1.
The ratio of
1:1 is most preferred.
The Use of the Additive (Second Aspect of the Invention) and Method (fourth
Aspect of
the Invention)
The preferred additives for the second and fourth aspects of the invention are
those hereinbefore described in relation to the first aspect.
The fuel oil of the second and fourth aspects of the invention is preferably
that
hereinbefore described in relation to the first aspect.
The Use of the Fuel Composition (Third Aspect of the Invention)
Where the fuel oil is diesel fuel, the fuel oil composition of the first
aspect of the
invention finds application in diesel (compression-ignition) engines as a fuel
which, in
addition to providing good combustion properties, reduces the wear rate in the
fuel supply
system, and particularly in the fuel injection pump. Use of the fuel thus
prolongs the
~iorking life of the equipment and reduces the need for replacement of
expensive
n'iechanical parts.
The fuel oil composition of the first aspect of the invention similarly finds
application in other fuel oil systems wherein the mechanical devices in the
fuel supply
system are reliant upon the fuel oil for lubrication, and are accordingly
subject to wear.
Croncentrates
~~- -
Concentrates comprising the additive in admixture with a carrier liquid (e.g.
as a
s)lution or a dispersion) are convenient as a means for incorporating the
additive into bulk
fiael oil, which incorporation may be done by methods known in the art. The
concentrates
ni~ay also contain other additives as required and preferably contain from 3
to 75 wt %,
n1ore preferably 3 to 60 wt %, most preferably 10 to 50 wt % of the additives
preferably in
solution in oil. Examples of carrier liquid are organic solvents including
hydrocarbon
solvents, for example petroleum fractions such as naphtha, kerosene, diesel
and heater
'~',
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oil; aromatic hydrocarbons such as aromatic fractions, e.g. those sold under
the
'SOLVESSO' tradename; paraffinic hydrocarbons such as hexane and pentane and
isoparaffins; and oxygenated solvents such as alcohols. The carrier liquid
must, of
course, be selected having regard to its compatibility with the additive and
with the fuel.
The concentrates are added to the bulk fuel oil in amounts sufficient to
supply the treat
rate of additive hereinbefore indicated.
The additives of the invention may be incorporated into bulk fuel oil by other
methods such as those known in the art. If co-additives are required, they may
be
incorporated into the bulk fuel oil at the same time as the additives of the
invention or at a
different time.
Co-additives
The fuel composition of the first aspect of the invention may additionally
comprise
other known lubricity-enhancing compounds as co-additives, for example mono-
or
polycarboxylic acids, such as dicarboxylic acids. These acids are preferably
mixtures of
polymerised unsaturated fatty acids, comprising mainly dimer and some trimer
acid, with
minor proportions of monomer and/or higher polymers. Typical examples are the
dimer
acids of oleic acid, linoleic acid or mixtures thereof. Esters of these acids
with
monohydric or dihydric alcohols may also be used in combination with the
mixture of
esters (a) and (b), to give further improved additives.
Similarly, ethoxylated-amine type lubricity co-additives may be used.
The fuel oil of the first aspect of the invention may also advantageously
comprise
one or more fuel oil cold flow improvers, as co-additives, such as one or more
of:
(i) ethylene-unsaturated ester copolymers,
(ii) hydrocarbon polymers,
(iii) sulphur carboxy compound,
(iv) polar compounds,
(v) hydrocarbylated aromatics,
(vi) linear compounds, and
(vii) comb polymers
as hereinafter defined.
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(i) Ethylene-Unsaturated Ester Copolymer
Ethylene copolymer flow improvers e.g. ethylene unsaturated ester copolymer
flow
improvers, have a polymethylene backbone divided into segments by hydrocarbyl
side
chains interrupted by one or more oxygen atoms and/or carbonyl groups.
More especially, the copolymer may comprise an ethylene copolymer having, in
addition to units derived from ethylene, units of the formula
-CR5R6-CHR7-
wherein R6 represents hydrogen or a methyl group; R5 represents a-OOCR8 or -
COOR8
group wherein R8 represents hydrogen or a Cl to Cg, preferably C1 to C6, more
preferably C1 to C3, straight or branched chain alkyl group; and R7 represents
hydrogen
or a -COOR8 or -OOCR8 group.
These may comprise a copolymer of ethylene with an ethylenically unsaturated
ester, or derivatives thereof. An example is a copolymer of ethylene with an
ester of an
unsaturated carboxylic acid such as ethylene - acrylates (e.g. ethylene -2-
ethylhexylacrylate), but the ester is preferably one of an unsaturated alcohol
with a
saturated carboxylic acid such as described in GB-A-1,263,152. An ethylene-
vinyl ester
copolymer is advantageous; an ethylene-vinyl acetate, ethylene vinyl
propionate,
ethylene-vinyl hexanoate, ethylene 2-ethylhexanoate, or ethylene-vinyl
octanoate
copolymer is preferred. Preferably, the copolymers contain from 1 to 25 such
as less
than 25, e.g. 1 to 20, mole % of the vinyl ester, more preferably from 3 to 15
mole % vinyl
ester. They may also be in the form of mixtures of two copolymers such as
those
described in US-A-3,961,916 and EP-A-113,581. Preferably, number average
molecular
weight, as measured by vapour phase osmometry, of the copolymer is 1,000 to
10,000,
more preferably 1,000 to 5,000. If desired, the copolymers may be derived from
additional comonomers, e.g. they may be terpolymers or tetrapolymers or higher
polymers, for example where the additional comonomer is isobutylene or
diisobutylene or
another ester giving rise to different units of the above formula and wherein
the above-
mentioned mole %'s of ester relate to total ester.
Also, the copolymers may include small proportions of chain transfer agents
and/or molecular weight modifiers (e.g. acetaidehyde or propionaldehyde) that
may be
used in the polymerisation process to make the copolymer.
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The copolymers may be made by direct polymerisation of comonomers. Such
copolymers may also be made by transesterification, or by hydrolysis and re-
esterification, of an ethylene unsaturated ester copolymer to give a different
ethylene
unsaturated ester copolymer. For example, ethylene vinyl hexanoate and
ethylene vinyl
octanoate copolymers may be made in this way, e.g. from an ethylene vinyl
acetate =
copolymer.
The copolymers may, for example, have 15 or fewer, preferably 10 or fewer,
more
preferably 6 or fewer, most preferably 2 to 5, methyl terminating side
branches per 100
methylene groups, as measured by nuclear magnetic resonance, other than methyl
groups on a comonomer ester and other than terminal methyl groups.
The copolymers may have a polydispersity of 1 to 6 preferably 2 to 4,
polydispersity being the ratio of weight average molecular wright to number
average
molecular wright both as measured by Gel Permeation Chromatography using
polystyrene standards.
(ii) Hydrocarbon Polymers
Linear Hydrocarbon Polymers
These have one or more polymethylene backbones, optionally divided into
segments by short chain length hydrocarbyl groups, i.e. of 5 or less carbon
atoms.
Examples are those represented by the following general formula
~CTT - CHT CHU - CHU
~ ~7
v w
where T represents H or R1;
U represents H, T or substituted or unsubstituted aryl; and
R1 represents a hydrocarbyl group having up to 5 carbon atoms.
and v and w represent mole ratios, v being within the range 1.0 to 0.0, w
being within the
range 0.0 to 1Ø Preferably, R1 is a straight or branched chain alkyl group.
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These polymers may be made directly from ethylenically unsaturated monomers
or indirectly by hydrogenating the polymer made from monomers such as isoprene
and
butadiene.
Preferred hydrocarbon polymers are copolymers of ethylene and at least one a-
olefin. Examples of such olefins are propylene, 1-butene, isobutene, and 2, 4,
4-
trimethylpent-2 -ene. The copolymer may also comprise small amounts, e.g. up
to 10%
by weight of other copolymerizable monomers, for example olefins other than a-
olefins,
and non-conjugated dienes. The preferred copolymer is an ethylene-propylene
copolymer. It is within the scope of the invention to include two or more
different
ethylene-a-olefin copolymers of this type.
The number average molecular weight of the ethylene-a-olefin copolymer is less
than 150,000, as measured by gel permeation chromatography (GPC) relative to
polystyrene standards. For some applications, it is advantageously at least
60,000 and
preferably at least 80,000. Functionally no upper limit arises but
difficulties of mixing
result from increased viscosity at molecular weights above about 150,000, and
preferred
molecular weight ranges are from 60,000 and 80,000 to 120,000. For other
applications,
it is below 30,000, preferably below 15, 000 such as below 10,000 or below
6,000.
Advantageously, the copolymer has a molar ethylene content between 50 and 85
per cent. More advantageously, the ethylene content is within the range of
from 55 to
80%, and preferably it is in the range from 55 to 75%; more preferably from 60
to 70%,
and most preferably 65 to 70%.
Examples of ethylene-a-olefin copolymers are ethylene-propylene copolymers
with a molar ethylene content of from 60 to 75% and a number average molecular
weight
in the range 60,000 to 120,000, especially preferred copolymers are ethylene-
propylene
copolymers with an ethylene content of from 62 to 71 % and a molecular weight
from
80,000 to 100,000.
The copolymers may be prepared by any of the methods known in the art, for
example using a Ziegler type catalyst. Advantageously, the polymers are
substantially
. amorphous, since highly crystalline polymers are relatively insoluble in
fuel oil at low
temperatures.
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(iii) Sultahur Carboxy Compounds
Examples are those described in EP-A-0,261,957 which describes the use of .
compounds of the general formula
.
A X-R1
C
B/ Y-R2
in which -Y-R2 is SO3(-)(+)NRJR2, -S03(-)(+)HNR~R2, -SO3(-)(+)H2NR3R2,
-SO3(-)(+)H3NR2, -SO2NR3R2 or -S03R2; and -X-R1 is -Y-R2 or -CONR3R1,
-CO2(-)(+)NRJR1, -CO2(-)(+)HNR3R1, -R4-COOR1, -NR3COR1, -R40R1, -R4OCOR1, -
R4,R1, -N(COR3)R1 or Z(-)(+)NRJR1; -Z(-) is SO3(-) or -C02(-);
R1 and R2 are alkyl, alkoxyalkyl or polyalkoxyalkyl containing at least 10
carbon
atoms in the main chain;
R3 is hydrocarbyl and each R3 may be the same or different and R4 is absent or
is C1 to C5 alkylene and in
A~
C
I
C
B
the carbon-carbon (C-C) bond is either a) ethylenically unsaturated when A and
B may be
alkyl, alkenyl or substituted hydrocarbyl groups or b) part of a cyclic
structure which may
be aromatic, polynuclear aromatic or cyclo-aliphatic, it is preferred that X-
R1 and Y-R2
between them contain at least three alkyl, alkoxyalkyl or polyalkoxyalkyl
groups.
Multicomponent additive systems may be used and the ratios of additives to be
used will depend on the fuel to be treated.
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(iv) Polar Com op unds
Such compounds comprise an oil-soluble polar nitrogen compound carrying one or
more, preferably two or more, hydrocarbyl substituted amino or imino
substituents, the
hydrocarbyl group(s) being monovalent and containing 8 to 40 carbon atoms,
which
substituent or one or more of which substituents optionally being in the form
of a cation
derived therefrom. The oil-soluble polar nitrogen compound is either ionic or
non-ionic
and is capable of acting as a wax crystal growth modifier in fuels.
Preferably, the
hydrocarbyl group is linear or slightly linear, i.e. it may have one short
length (1-4 carbon
atoms) hydrocarbyl branch. When the substituent is amino, it may carry more
than one
said hydrocarbyl group, which may be the same or different.
The term "hydrocarbyl" refers to a group having a carbon atom directly
attached to
the rest of the molecule and having a hydrocarbon or predominantly hydrocarbon
character. Examples include hydrocarbon groups, including aliphatic (e.g.
alkyl or
alkenyl), alicyclic (e.g. cycloalkyl or cycloalkenyl), aromatic, and alicyclic-
substituted
aromatic, and aromatic-substituted aliphatic and alicyclic groups. Aliphatic
groups are
advantageously saturated. These groups may contain non-hydrocarbon
substituents
provided their presence does not alter the predominantly hydrocarbon character
of the
group. Examples include keto, halo, hydroxy, nitro, cyano, alkoxy and acyl. If
the
hydrocarbyl group is substituted, a single (mono) substituent is preferred.
Examples of substituted hydrocarbyl groups include 2-hydroxyethyl,
3-hydroxypropyl, 4-hydroxybutyl, 2-ketopropyl, ethoxyethyl, and propoxypropyl.
The
groups may also or alternatively contain atoms other than carbon in a chain or
ring
otherwise composed of carbon atoms. Suitable hetero atoms include, for
example,
nitrogen, sulphur, and, preferably, oxygen.
More especially, the or each amino or imino substutent is bonded to a moiety
via
an intermediate linking group such as -CO-, -C02(-), -S03(-) or
hydrocarbylene. Where
the linking group is anionic, the substituent is part of a cationic group, as
in an amine salt
. group.
. When the polar nitrogen compound carries more than one amino or imino
substituent, the linking groups for each substituent may be the same or
different.
Suitable amino substituents are long chain C12-C40, preferably C12-C24, alkyl
primary, secondary, tertiary or quaternary amino substituents.
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Preferably, the amino substituent is a dialkylamino substituent, which, as
indicated
above, may be in the form of an amine salt thereof; tertiary and quaternary
amines can
form only amine salts. Said alkyl groups may be the same or different.
Examples of amino substituents include dodecylamino, tetradecylamino,
cocoamino, and hydrogenated tallow amino. Examples of secondary amino
substituents
include dioctadecylamino and methylbehenylamino. Mixtures of amino
substituents may
be present such as those derived from naturally occurring amines. A preferred
amino
substituent is the secondary hydrogenated tallow amino substituent, the alkyl
groups of
which are derived from hydrogenated tallow fat and are typically composed of
approximately 4% C1 q,, 31 % C1 g and 59% C1 g n-alkyl groups by weight.
Suitable imino substituents are long chain C12-C40, preferably C12-C24, alkyl
substituents.
Said moiety may be monomeric (cycylic or non-cyclic) or polymeric. When non-
cyclic, it may be obtained from a cyclic precursor such as an anhydride or a
spirobislactone.
The cyclic ring system may include homocyclic, heterocyclic, or fused
polycyclic
assemblies, or a system where two or more such cyclic assemblies are joined to
one
another and in which the cyclic assemblies may be the same or different. Where
there
are two or more such cyclic assemblies, the substituents may be on the same or
different
assemblies, preferably on the same assembly. Preferably, the or each cyclic
assembly is
aromatic, more preferably a benzene ring. Most preferably, the cyclic ring
system is a
single benzene ring when it is preferred that the substituents are in the
ortho or meta
positions, which benzene ring may be optionally further substituted.
The ring atoms in the cyclic assembly or assemblies are preferably carbon
atoms
but may for example include one or more ring N, S or 0 atom, in which case or
cases the
compound is a heterocyclic compound. Examples of such polycyclic assemblies
include =
(a) condensed benzene structures such as naphthalene, anthracene,
phenanthrene, and pyrene;
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(b) condensed ring structures where none of or not all of the rings are
benzene such as azulene, indene, hydroindene, fluorene, and diphenylene
oxides:
(c) rings joined "end-on" such as diphenyl;
(d) heterocyclic compounds such as quinoline, indole, 2:3 dihydroindole,
benzofuran, coumarin, isocoumarin, benzothiophen, carbazole and
thiodiphenylamine;
(e) non-aromatic or partially saturated ring systems such as decalin (i.e.
decahydronaphthalene), a-pinene, cardinene, and bomylene; and
(f) three-dimensional structures such as norbomene, bicycloheptane (i.e.
norbomane), bicyclooctane, and bicyclooctene.
Examples of polar nitrogen compounds are described below:
(I) an amine salt and/or amide of a mono- or poly-carboxylic acid, e.g. having
1 to 4 carboxylic acid groups. It may be made, for example, by reacting at
least one molar proportion of a hydrocarbyl substituted amine with a molar
proportion of the acid or its anhydride.
When an amide is formed, the linking group is -CO-, and when an amine
salt is formed, the linking group is -C02(-).
The moiety may be cyclic or non-cyclic. Examples of cyclic moieties are
those where the acid is cyclohexane 1,2-dicarboxylic acid; cyclohexane
1,2-dicarboxylic acid; cyclopentane 1,2-dicarboxylic acid; and naphthalene
dicarboxylic acid. Generally, such acids have 5 to 13 carbon atoms in the
cyclic moiety. Preferred such cyclic acids are benzene dicarboxylic acids
such as phthalic acid, isophthalic acid, and terephthalic acid, and benzene
tetracarboxylic acids such as pyromelletic acid, phthalic acid being
particularly preferred. US-A-4,211,534 and EP-A-272,889 describes polar
nitrogen compounds containing such moieties.
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Examples of non-cyclic moieties are those when the acid is a long chain
alkyl or alkylene substituted dicarboxylic acid such as a succinic acid, as
described in US-A-4,147,520 for example.
Other examples of non-cyclic moieties are those where the acid is a
nitrogen-containing acid such as ethylene diamine tetracetic acid.
Further examples are the moieties obtained where a dialkyl spirobislactone
is reacted with an amine.
(II) EP-A-0,261,957 describes polar nitrogen compounds according to the
present description of the general formula
A X-R1
\C/
I
B/ \Y-R2
in which -Y-R2 is S03(-)(+)NR3R2, -SO3(-)(+)HNR3R2, -
S03(-)(+)H2NR3R2,
-SO3(-)(+)H3NR2, -SO2NR3R2 or -S03R2; and -X-R1 is -Y-R2 or
-CONR3R1,
-CO2(-)(+)NRRR1, -CO2(-)(+)HNR3R1, -R4-COOR1, -NR3COR1,
-R40R1, -R4OCOR1, -R4,R1, -N(COR3)R1 orZ(-)(+)NRJR1; -Z(-) is
S03(-) or -C02(-);
Rl and R2 are alkyl, alkoxyalkyl or polyalkoxyalkyl containing at least 10
carbon atoms in the main chain;
R3 is hydrocarbyl and each R3 may be the same or different and R4 is
absent or is C1 to C5 alkylene and in
C
(
C
B
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the carbon-carbon (C-C) bond is either a) ethylenically unsaturated when A
and B may be alkyl, alkenyl or substituted hydrocarbyl groups or b) part of
a cyclic structure which may be aromatic, polynuclear aromatic or cyclo-
aliphatic, it is preferred that X-RI and Y-R2 between them contain at least
three alkyl, alkoxyalkyl or polyalkoxyalkyl groups.
Multicomponent additive systems may be used and the ratios of additives
to be used will depend on the fuel to be treated.
(III) EP-A-0,316,108 describes an amine or diamine salt of (a) a
sulphosuccinic
acid, b) an ester or diester of a sulphosuccinic acid, c) an amide or a
diamide of a sulphosuccinic acid, or d) an ester-amide of a sulphosuccinic
acid.
(IV) A chemical compound comprising or including a cyclic ring system, the
compound carrying at least two substituents of the general formula (I)
below on the ring system
-A-NR1 R2 (I)
where A is an aliphatic hydrocarbyl group that is optionally interrupted by
one or more hetero atoms and that is straight chain or branched, and Rl
and R2 are the same or different and each is independently a hydrocarbyl
group containing 9 to 40 carbon atoms optionally interrupted by one or
more hetero atoms, the substituents being the same or different and the
compound optionally being in the form of a salt thereof.
Preferably, A has from 1 to 20 carbon atoms and is preferably a methylene
or polymethylene group.
Each hydrocarbyl group constituting R1 and R2 in the invention (Formula
1) may for example be an alkyl or alkylene group or a mono- or poly-
alkoxyalkyl group. Preferably, each hydrocarbyl group is a straight chain
alkyl group. The number of carbon atoms in each hydrocarbyl group is
preferably 16 to 40, more preferably 16 to 24.
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Also, it is preferred that the cyclic system is substituted with only two
substituents of the general formula (I) and that A is a methylene group.
Examples of salts of the chemical compounds are the acetate and the
hydrochloride.
The compounds may conveniently be made by reducing the corresponding
amide which may be made by reacting a secondary amine with the
appropriate acid chloride.
(V) A condensate of long chain primary or secondary amine with a carboxylic
acid-containing polymer.
Specific examples include polymers such as described in GB-A-2,121,807,
FR-A-2,592,387 and DE-A-3,941,561; and also esters of telemer acid and
alkanoloamines such as described in US-A-4,639,256; and the reaction
product of an amine containing a branched carboxylic acid ester, an
epoxide and a mono-carboxylic acid polyester such as described in US-
A4,631,071.
EP-0,283,292 describes amide containing polymers and EP-0,343,981
describes amine-salt containing polymers.
It should be noted that the polar nitrogen compounds may contain other
functionality such as ester functionality.
(v) Hydrocarbylated Aromatics
These material are condensates comprising aromatic and hydrocarbyl parts. The
aromatic part is conveniently an aromatic hydrocarbon which may be
unsubstituted or
substituted with, for example, non-hydrocarbon substitutents.
.
Such aromatic hydrocarbon preferably contains a maximum of these substituent
groups and/or three condensed rings, and is preferably naphthalene. The
hydrocarbyl
part is a hydrogen and carbon containing part connected to the rest of the
molecule by a
carbon atom. It may be saturated or unsaturated, and straight or branched, and
may
contain one or more hetero-atoms provided they do not substantially affect the
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hydrocarbyl nature of the part. Preferably the hydrocarbyl part is an alkyl
part,
conveniently having more than 8 carbon atoms.
(vi) Linear Com on unds
Such compounds comprise a compound in which at least one substantially linear
alkyl group havirig 10 to 30 carbon atoms is connected via an optional linking
group that
may be branched to a non-polymeric residue, such as an organic residue, to
provide at
least one linear chain of atoms that includes the carbon atoms of said alkyl
groups and
one or more non-terminal oxygen, sulphur and/or nitrogen atoms. The linking
group may
be polymeric.
By "substantially linear" is meant that the alkyl group is preferably straight
chain,
but that straight chain alkyl groups having a small degree of branching such
as in the form
of a single methyl group branch may be used.
Preferably, the compound has at- least two of said alkyl groups when the
linear
chain may include the carbon atoms of more than one of said alkyl groups. When
the
compound has at least three of said alkyl groups, there may be more than one
of such
linear chains, which chains may overlap. The linear chain or chains may
provide part of
the linking group between any two such alkyl groups in the compound.
The oxygen atom or atoms, if present, are preferably directly interposed
between
carbon atoms in the chain and may, for example, be provided in the linking
group, if
present, in the form of a mono- or poly-oxyalkylene group, said oxyalkylene
group
preferably having 2 to 4 carbon atoms, examples being oxyethylene and
oxypropylene.
As indicated the chain or chains include carbon, oxygen, sulphur and/or
nitrogen
atoms.
The compound may be an ester where the alkyl groups are connected to the
remainder of the compound as -0-CO n alkyl, or -CO-O n alkyl groups, in the
former the
alkyl groups being derived from an acid and the remainder of the compound
being derived
from a polyhydric alcohol and in the latter the alkyl groups being derived
from an alcohol
and the remainder of the compound being derived from a polycarboxylic acid.
Also, the
compound may be an ether where the alkyl groups are connected to the remainder
of the
compound as -O-n-alkyl groups. The compound may be both an ester and an ether
or it may contain different ester groups.
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Examples include polyoxyalkylene esters, ethers, ester/ethers and mixtures
thereof, particularly those containing at least one, preferably at least two,
C10 to C30
linear alkyl groups and a polyoxyalkylene glycol group of molecular weight up
to 5,000,
preferably 200 to 5,000, the alkylene group in said polyoxyalkylene glycol
containing from
1 to 4 carbon atoms, as described in EP-A-61 895 and in U.S. Patent No.
4,491,455.
The preferred esters, ethers or ester/ethers which may be used may comprise
compounds in which one or more groups (such as 2, 3 or 4 groups) of formula -
OR25 are
bonded to a residue E, where E may for example represent A (alkylene)q, where
A
represents C or N or is absent, q represents an integer from I to 4, and the
alkylene
group has from one to four carbon atoms, A (alkylene)q for example being
N(CH2CH2)3;
C(CH2)4; or (CH2)2; and R25 may independently be
(a) n-alkyl-
(b) n-alkyl-CO-
(c) n-alkyl-OCO-(CH2)n-
(d) n-alkyl-OCO-(CH2)nCO-
n being, for example, 1 to 34, the alkyl group being linear and containing
from 10 to 30
carbon atoms. For example, they may be represented by the formula R230BOR24,
R23
and R24 each being defined as for R25 above, and B representing the
polyalkylene
segment of the glycol in which the alkylene group has from 1 to 4 carbon
atoms, for
example, polyoxymethylene, polyoxyethylene or polyoxytrimethylene moiety which
is
substantially linear; some degree of branching with lower alkyl side chains
(such as in
polyoxypropylene glycol) may be tolerated but it is preferred that the glycol
should be
substantially linear.
Suitable glycols generally are substantially linear polyethylene glycols (PEG)
and
polypropylene glycols (PPG) having a molecular weight of about 100 to 5,000,
preferably
about 200 to 2,000. Esters are preferred and fatty acids containing from 10 to
30 carbon
atoms are useful for reacting with the glycols to form the ester additives, it
being preferred
to use C18 to C24 fatty acid, especially behenic acid. The esters may also be
prepared
by esterifying polyethoxylated fatty acids or polyethoxylated alcohols.
Polyoxyalkylene diesters, diethers, ether/esters and mixtures thereof are
suitable
as additives, diesters being preferred when the petroleum based component is a
narrow
boiling distillate, when minor amounts of monoethers and monoesters (which are
often
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formed in the manufacturing process) may also be present. It is important for
active
performance that a major amount of the dialkyl compound is present. In
particular, stearic
or behenic diesters of polyethylene glycol, polypropylene glycol or
polyethylene/polypropylene glycol mixtures are preferred.
Examples of other compounds in this general category are those described in
Japanese Patent Publication Nos. 2-51477 and 3-34790, and EP-A-1 17,108 and EP-
A-
326,356, and cyclic esterified ethoxylates such as described EP-A-356,256.
(vii) Comb Polymers
Comb polymers are discussed in "Comb-Like Polymers. Structure and
Properties", N. A. Plate and V. P. Shibaev, J. Poly. Sci. Macromolecular
Revs., 8, p 117
to 253 (1974).
Generally, comb polymers consist of molecules in which long chain branches
such
as hydrocarbyl branches, optionally interrupted with one or more oxygen atoms
and/or
carbonyl groups, having from 6 to 30 such as 10 to 30, carbon atoms, are
pendant from a
polymer backbone, said branches being bonded directly or indirectly to the
backbone.
Examples of indirect bonding include bonding via interposed atoms or groups,
which
bonding can include covalent and/or electrovalent bonding such as in a salt.
Generally,
comb polymers are distinguished by having a minimum molar proportion of units
containing such long chain branches.
Advantageously, the comb polymer is a homopolymer having, or a copolymer at
least 25 and preferably at least 40, more preferably at least 50, molar per
cent of the units
of which have, side chains containing at least 6 such as at least 8, and
preferably at least
10, atoms, selected from for example carbon, nitrogen and oxygen, in a linear
chain or a
chain containing a small amount of branching such as a single methyl branch.
As examples of preferred comb polymers there may be mentioned those
containing units of the general formula
~CDE - CHG CJK - CHL
m n
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where D represents R11, COOR11, OCOR11, R12COOR11 or OR11;
E represents H, D or R12;
G represents H or D;
J represents H, R12, R12COOR11, or a substituted or unsubstituted aryl or
heterocyclic group;
K represents H, COOR12, OCOR12, OR12 or COOH;
L represents H, R12, COOR12, OCOR12 or substituted or unsubstituted aryl;
R11 representing a hydrocarbyl group having 10 or more carbon atoms, and
R12 representing a hydrocarbyl group being divalent in the 12COOR1 1 group
and otherwise being monovalent,
and m and n represent mole ratios, their sum being 1 and m being finite and
being up to
and including 1 and n being from zero to less than 1, preferably m being
within the range
of from 1.0 to 0.4, n being in the range of from 0 to 0.6. R11 advantageously
represents a
hydrocarbyl group with from 10 to 30 carbon atoms, preferably 10 to 24, more
preferably
10 to 18. Preferably, R11 is a linear or slightly branched alkyl group and R12
advantageously represeiits a hydrocarbyl group with from 1 to 30 carbon atoms
when
monovalent, preferably with 6 or greater, more preferably 10 or greater,
preferably up to
24, more preferably up to 18 carbon atoms. Preferably, R12, when monovalent,
is a
linear or slightly branched alkyl group. When R12 is divalent, it is
preferably a methylene
or ethylene group. By "slightly branched" is meant having a single methyl
branch.
The comb polymer may contain units derived from other monomers if desired or
required, examples being CO, vinyl acetate and ethylene. It is within the
scope of the
invention to include two or more different comb copolymers.
The comb polymers may, for example, be copolymers of maleic anhydride or
fumaric acid and another ethylenically unsaturated monomer, e.g. an a-olefin
or an
unsaturated ester, for example, vinyl acetate as described in EP-A-214,786. It
is
preferred but not essential that equimolar amounts of the comonomers be used
although
molar proportions in the range of 2 to 1 and 1 to 2 are suitable. Examples of
olefins that
may be copolymerized with e.g. maleic anhydride, include 1-decene, 1-dodecene,
1-
tetradecene, 1-hexadecene, 1-octadecene, and styrene. Other examples of comb
polymer include methacrylates and acrylates.. '
The copolymer may be esterified by any suitable technique and although
preferred
it is not essential that the maleic anhydride or fumaric acid be at least 50%
esterified.
Examples of alcohols which may be used include n-decan-l-ol, n-dodecan-l-ol, n-
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tetradecan-l-ol, n-hexadecan-l-ol, and n-octadecan-l-ol. The alcohols may also
include
up to one methyl branch per chain, for example, 1-methylpentadecan-1-ol, 2-
methyltridecan-l-ol as described in EP-A-213,879. The alcohol may be a mixture
of
normal and single methyl branched alcohols. It is preferred to use pure
alcohols rather
than alcohol mixtures such as may be commerically available; if mixtures are
used the
number of carbon atoms in the alkyl group is taken to be the average number of
carbon
atoms in the alkyl groups of the alcohol mixture; if alcohols that contain a
branch at the 1
or 2 positions are used the number of carbon atoms in the alkyl group is taken
to be the
number in the straight chain backbone segment of the alkyl group of the
alcohol.
The comb polymers may especially be fumarate or itaconate polymers and
copolymers such as for example those described in European Patent Applications
153 176, 153 177, 156 577 and 225 688, and WO 91/16407.
Particularly preferred fumarate comb polymers are copolymers of alkyl
fumarates
and vinyl acetate, in which the alkyl groups have from 12 to 20 carbon atoms,
more
especially polymers in which the alkyl groups have 14 carbon atoms or in which
the alkyl
groups are a mixture of C14/C16 alkyl groups, made, for example, by solution
copolymerizing an equimolar mixture of fumaric acid and vinyl acetate and
reacting the
resulting copolymer with the alcohol or mixture of alcohols, which are
preferably straight
chain alcohols. When the mixture is used it is advantageously a 1:1 by weight
mixture of
normal C14 and C16 alcohols. Furthermore, mixtures of the C14 ester with the
mixed
C14/C16 ester may advantageously be used. In such mixtures, the ratio of C14
to
C14/C16 is advantageously in the range of from 1:1 to 4:1, preferably 2:1 to
7:2, and
most preferably about 3:1, by weight. The particularly preferred fumarate comb
polymers
may, for example, have a number average molecular weight in the range of 1,000
to
100,000, preferably 1,000 to 50,000, as measured by Vapour Phase Osmometry
(VPO).
Other suitable comb polymers are the polymers and copolymers of a-olefins and
esterified copolymers of styrene and maleic anhydride, and esterified
copolymers of
styrene and fumaric acid as described in EP-A-282,342; mixtures of two or more
comb
polymers may be used in accordance with the invention and, as indicated above,
such
use may be advantageous.
Other examples of comb polymers are hydrocarbon polymers such as copolymers
of ethylene and at least one a-olefin, preferably the a-olefin having at most
20 carbon
atoms, examples being n-octene-1, iso octene-1, n-decene-1 and n-dodecene-1, n-
tetradecene-1 and n-hexadecene-1 (for example, as described in WO9319106.
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Preferably, the number average molecular weight measured by Gel Permeation
Chromatography against polystyrene standards of such a copolymer is for
example, up to
30,000 or up to 40,000. The hydrocarbon copolymers may be prepared by methods
known in the art, for example using a Ziegler type catalyst. Such hydrocarbon
polymers
may for example have an isotacticity of 75% or greater. y
Some of the hereinbefore described cold flow improver co-additives may provide
synergistic enhancements to lubricity performance when in combination with the
mixture
of esters (a) and (b).
Further co-additives which may be used are those known in the art, for example
detergents, antioxidants, corrosion inhibitors, dehazers, demulsifiers, metal
deactivators,
antifoaming agents, combustion improvers such as cetane improvers, co-
solvents,
package compatibilisers, reodorants and metallic-based additives such as
metallic
combustion improvers.
Assessment of the Benefits of the Various Aspects of the Invention
It is believed that the mixture of esters (a) and (b) is capable of forming at
least
partial layers of a lubricating composition on certain metal surfaces. By this
is meant that
the layer formed is not necessarily compiete on the contacting surface. The
formation of
such layers and the extent of their coverage of a contacting surface can be
demonstrated
by, for example, measuring electrical contact resistance or electrical
capacitance.
A test that can be used to demonstrate one or more of a reduction in wear, a
reduction in friction or an increase in electrical contact resistance
according to this
invention is the High Frequency Reciprocating Rig test (or "HFRR"), described
in the
standard test methods CEC PF 06-T-94 or ISO/TC22/SC7/WG6/N188.
The extent to which an additive composition causes blocking of fuel oil line
filters
can be measured using a known filterability test. For example, a method for
measuring
the filterability of fuel oil compositions is described in the Institute of
Petroleum's Standard
designated "IP 387/190" and entitled "Determination of filter blocking
tendency of gas oils
and distillate diesel fuels". In summary, a sample of the fuel oil composition
to be tested
is passed at a constant rate of flow through a glass fibre filter medium; the
pressure drop
across the filter is monitored, and the volume of fuel oil passing the filter
medium within a
prescribed pressure drop is measured. The filter blocking tendency of a fuel
composition
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can be described as the pressure drop across the filter medium for 300 mi of
fuel to pass
at a rate of 20 ml/min. Reference is to be made to the above-mentioned
Standard for
, further information. In assessing the additive composition of the present
invention this
method was adapted by conducting the measurements at various temperatures
lower
, 5 than that specified in the Standard, to simulate cold storage conditions
which occur in the
field.
The invention is further illustrated by reference to the following Examples.
Example I
The following materials and procedures were used.
Fue1Oi1
A 'Class I' diesel fuel oil having the characteristics shown below:
Sulphur: 4.5 ppm wt/wt
Cetane Number: 51.6
CFPP (Auto) -36 C
Distillation: 50% Evaporation 237.1 C
Final Boiing Point 294.1 C
Residue (% vol.) 1.2
Additives
Additives A, B, C and D were added to the diesel fuel oil in the amounts
recorded
in Table 1, and the filterability of each of the fuel compositions was
assessed according to
the IP 387/90 test at the temperatures shown in Table 1. In each case, after
thorough
mixing, the sample fuel composition was cooled to the required temperature in
a
refrigeration unit and stored at that temperature for the stated period of
time before being
subject to the filtration test.
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_
a a5 N N Y :M
Q- C ~, a
r~.. 3 N C'~
CO '
N
~
Q N '-- N tp 0)
~ N N
ti G C
c'; v E E
O
Z
to cu
Y d Y Q a-~-
~ F- N f-
N G_
r.. Kj V~ N
LL7
cu m
~p C -1C CL M
O rn c
ces E ~
tCA L
~
C13
(a ca _ QD
m Y u~ Y y p ~ - n
o ti ti ~ c~
e- r..
W Q ~ M N N U)
m ca
N
E
~ a .-~ -. a ~ -~
~ a ~c Q Y Q -
N
(p 0) O ' ' w
c~ OO 0
C6
.N
0
0
iL
O
R '3
>
'4d
v .,;
VE d Z N N N N
a
>v,
~a =
m
>
= ~
-~a z ~ o U o
a-
Q.
E CV cl)
c4
~
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Additive A was prepared by esterification of a commercial mixture of oleic and
linoleic acids with glycerol, to produce a mixed ester product predominating
in (a) glycerol
monooleate and (b) glycerol monolinoleate, in approximately equal proportions
by weight,
with minor amounts of glycerol di- and trioleate and linoleate also present.
In addition, the
= 5 acid mixture contained a minor proportion of other acids, the esters of
which were not
believed to represent more than about 6% by weight of the mixed ester product.
Additive B was prepared by esterification of oleic acid with glycerol, to form
a
product predominating in glycerol monooleate (Additive D of WO 94/17160).
Additive C was prepared by esterification of linoleic acid with glycerol, to
form a
product predominating in glycerol monolinolate.
Additive D was a 1:1 molar mixture of Additive B and Additive C.
In Table 1, the test results indicate the pressure drop over the filter at the
end of
each test, higher pressure drops indicating a greater degree of partial filter
blocking.
Where the pressure drop became larger than 103.4 kPa (15 psi) during the 15
minute
test, the test time at which this pressure was reached was recorded (103.4
kPa, i.e. 15
psi, corresponds to severe filter blocking and is regarded for these purposes
as a test
'fail').
It can be seen from the results in Table 1 that Sample 2 (fuel composition of
the
invention) showed surprisingly improved filterability over Sample 3
(comparative fuel
composition containing additive D of WO 94/17160), both at 0 C and -10 C.
Furthermore,
although both examples exceeded 103.4 kPa in the test after 1 week at -10 C,
Sample 2
was a better performer (exceeded just before the end of the 15 minute test in
contrast to
Sample 3 which exceeded this pressure drop almost immediately).
Furthermore, the results at -5 C indicate that Samples 2 and 5 (fuel
compositions
of the invention) showed greatly improved filterability over Samples 3 and 4
(comparatives), these two comparative examples both failing the test. Sample 2
containing Additive A (made by esterifying a mixture of starting acids) also
showed
= surprisingly improved performance in comparison to Sample 5 containing
Additive D
(made by mixing together the component esters).
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Example 2
A small aliquot of each of the Samples of Example 1 stored at -5 C for 2 weeks
was removed immediately prior to the filtration step described in Example 1,
and the
HFRR performance at 60 C of each aliquot measured as an indication of 'pre-
filtration' =
lubricity performance. The HFRR performance at 60 C of each corresponding
sample
filtrate produced in Example I was also measured as an indication of 'post-
filtration'
lubricity performance. The results are compared in Table 2 below.
Table 2
Additive
Concentration HFRR HFRR
(ppm active Wear Scar Wear Scar
Sample Additive ingredient, wt/wt) Before Fiitration (pm) After Filtration
(pm)
1 None Nil 623 610
2 A 200 309 330
3 B 200 249 396
4 C 200 343 411
5 D 200 292 274
The results in Table 2 indicate that Samples 3 and 4 (comparatives) show
significantly poorer lubricity performance after filtration (i.e. a larger
wear scar), in contrast
to Samples 2 and 5 (fuel compositions of the invention) which maintained their
lubricity
performance.
The untreated fuel (Sample 1) showed no change, confirming that the
differences
in the results of other samples are due to the additives present in these
compositions.
The differences in wear scar diameter after filtration indicate a significant
technical
improvement and demonstrate the improved lubricity properties provided by
mixtures of
esters (a) and (b), over comparative additives.
