Note: Descriptions are shown in the official language in which they were submitted.
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Fuel Oil Comnositions
FIELD OF THE INVENTION
This invention relates to improvements in fuel oil compositions, more
especially
to fuel oil compositions containing detergent species and that are susceptible
to wax
formation at low temperatures.
BACKGROUND OF THE INVENTION
Fuel oils, whether derived from petroleum or from vegetable sources, contain
components, e.g., n-alkanes or methyl n-alkanoates, that at low temperature
tend to
precipitate as large, plate-like crystals or spherulites of wax in such a way
as to form a
gel structure which causes the fuel to lose its ability to flow. The lowest
temperature at
which the fuel will still flow is known as the pour point.
As the temperature of a fuel falls and approaches the pour point, difficulties
arise
in transporting the fuel through lines and pumps. Further, the wax crystals
tend to plug
fuel lines, screens, and filters at temperatures above the pour point. These
problems are
well recognised in the art, and various additives have been proposed, many of
which are
in commercial use, for depressing the pour point of fuel oils. Similarly,
other additives
have been proposed and are in commercial use for reducing the size and
changing the
shape of the wax crystals that do form. Smaller size crystals are desirable
since they are
less likely to clog a filter. The wax from a diesel fuel, which is primarily
an alkane wax,
crystallizes as platelets. Certain additives inhibit this and cause the wax to
adopt an
acicular habit, the resulting needles being more likely than platelets to pass
through a
filter or to form a porous layer of crystals on the filter. Other additives
may also have
the effect of retaining the wax crystals in suspension in the fuel, reducing
settling and
thus also assisting in preventing blockages. These types of additives are
often termed
'wax anti-settling additives' (WASA) and are commonly polar nitrogen species.
Many additives have been described for enhancing engine cleanliness, e.g. for
reducing or removing deposits in the intake system (e.g. carburettors, intake
manifold,
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inlet valves) or combustion chamber surfaces of spark-ignition engines, or for
reducing
or preventing injector nozzle fouling in compression-ignition engines.
For example, UK Patent No 960,493 describes incorporating metal-free
detergents, in the form of polyolefin-substituted succinimides of
tetraethylene
pentamine, in base fuels for internal combustion engines. The use of such
metal-free
detergents is now widespread. Most commonly used are polyisobutylene-
substituted
succinimides, which are the reaction products of polyisobutylene-substituted
acylating
agents such as succinic acid or anhydride with polyamines. Such materials and
their
methods of production are known to those skilled in the art. They may be
generally
described as metal-free polyalkylene amine detergents.
A trend in modern diesel engine technology is to increase power output and
efficiency by increasing injection pressures and decreasing injector nozzle
diameters.
Under these conditions, the build-up of injector deposits is more likely and
the
deposition which occurs is more severe. This has led fuel manufacturers to
produce new
types of fuels which are often sold as 'premium' grades and promoted as being
especially effective to improve engine cleanliness. To meet this performance
claim,
such premium fuels usually contain significantly higher levels of detergent
than non-
premium grade fuels.
Although largely effective with regard to engine cleanliness, a drawback has
been identified in the use of high levels of detergent in fuel oils.
Specifically, it has been
observed that the presence of high levels of polyalkylene amine detergents in
premium
grade fuels can interfere with the cold-flow performance of wax anti-settling
additives
when these are also present in the fuel. So, although the fuel may be
satisfactory for
engine cleanliness, its low temperature properties in terms of wax anti-
settling and cold
filter plugging point (CFPP) may not be adequate.
EP-A-0 908 507 describes the use of additives for improving the cold flow
properties of fuel oils, such as middle distillate fuel oil boiling within the
range of
110 C to 500 C. In the examples it describes fuels containing as additives an
N,N-
dialkylammonium salt of 2-N',N'-dialkyl-amido benzoate, being the reaction
product of
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i = .
PF2006M016 FF
3
reacting one mole of phthalic anhydride with two moles of dihydrogenated
tallow amine
to form a half amide/half amine salt (additive C and a constituent of
components BX
and BY therein); and a polyaminated polyisobutylene succinic anhydride
detergent (a
constituent of component AY therein). EP-A-0 908 507 describes the results of
simulated filter plugging point (SFPP) tests carried out on such fuels.
Additive C is an
example of a conventional wax anti-settling additive.
The present invention is based on the discovery that the use of a quaternary
ammonium salt of a polycarboxylic acid as a wax anti-settling additive in
place of a
conventional wax anti-settling additive can improve the low temperature
properties of
the fuel containing a polyalkylene amine detergent.
SUMMARY OF THE INVENTION
Thus, in accordance with a first aspect, the present invention provides a fuel
oil
composition comprising a major amount of a middle-distillate fuel oil
composition
comprising minor amounts of
(A) at least one oil-soluble polar nitrogen compound effective as a wax
anti-settling additive in the form of a quatemary ammonium salt of a
polycarboxylic acid; and
(B) at least one oil-soluble polyalkylene amine detergent,
wherein the concentrations of (A) and (B) are such that one or more of the low
temperature properties of said fuel oil composition are better than those of
an otherwise
identical fuel oil composition that contains, in place of (A), (Aref), which
is not a
quatemary ammonium salt and is an oil-soluble amine salt of a polycarboxylic
acid
analogous to (A); and
wherein the concentration of (B) in said fuel oil composition is such that it
would adversely affect one or more of the low temperature properties of (Aref)
in said
otherwise identical fuel oil composition.
Y
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In accordance with a second aspect, the present invention provides the use, in
a
middle distillate fuel oil composition comprising a minor amount of (B), which
is at
least one oil-soluble polyalkylene amine detergent, of a minor amount of (A),
which is
at least one oil-soluble polar nitrogen compound effective as a wax anti-
settling additive
in the form of a quaternary ammonium salt of a polycarboxylic acid, to improve
one or
more of the low temperature properties of said fuel oil composition in
comparison with
one or more of the low temperature properties of an otherwise identical fuel
oil
composition that contains, in place of (A), (Aref), which is not a quaterrnary
ammonium
salt and is an amine salt of a polycarboxylic acid analogous to (A), wherein
the
concentration of (B) in said fuel oil composition is such that it would
adversely affect
one or more of the low temperature properties of (Aref) in said otherwise
identical fuel
oil composition.
In accordance with a third aspect, the present invention provides a method of
making a middle distillate fuel oil composition comprising minor amounts of at
least
one polar nitrogen compound effective as a wax anti-settling additive and at
least one
polyalkylene amine detergent, which method comprises
(i) determining concentrations of (B), as defined in the first aspect of
the invention, and of (Aref), as defined in the first aspect of the
invention, at which (B) adversely effects one or more of the low
temperature properties of (Aref) in a middle distillate fuel oil
composition;
(ii) determining concentrations of (A), as defined in the first aspect of
the invention, at which one or more of the low temperature
properties of a middle distillate fuel oil composition containing
(B) at concentrations determined in step (i) are better than those of
an otherwise identical middle distillate fuel oil composition
containing (Aref) and (B); and
(iii) blending a middle distillate fuel oil composition containing (A)
and (B) in the concentrations determined in steps (i) and (ii).
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The observed loss in wax anti-settling and CFPP performance appears to be
limited to the use of metal-free polyalkylene amine detergents in combination
with
conventional WASA components. It is noteworthy that a similar loss in
performance
may not be observed when detergents other than polyalkylene amine detergents
are used
in combination with conventional WASA components. The addition of the
quatemary
ammonium salt mitigates this loss in performance thereby allowing higher
levels of
polyalkylene amine detergents to be used together with WASA species without
compromising the low temperature properties of the additised fuel.
As indicated above, the combined presence in a fuel oil of a polyalkylene
amine
detergent and a conventional WASA may lead to a reduction in performance in
terms of
wax anti-settling and/or CFPP. Better low temperature properties refers to
either wax
anti-settling performance or CFPP, or, preferably, to both properties.
Preferably one or
more low temperatUre properties of a fuel oil composition that contains a
conventional
WASA, but does not contain a polyalkylene amine detergent, are restored or
improved
by the present invention.
It should be noted that it is not required that either low temperature
property
necessarily reaches the level which would be expected without the presence of
a
polyalkylene amine detergent.
The use of the term 'restore' should be taken to include the situation where,
although the precise numerical value of the property may not be regained, the
difference
is not practically significant.
In accordance with a further aspect, the present invention provides a middle-
fuel oil composition comprising minor amounts of
distillate
(A) at least one oil-soluble polar nitrogen compound effective as a wax anti-
settling additive in the form of a quaternary ammonium salt of a phthalic
acid; and
(B) at least one polyalkylene amine detergent in the form of an N-
(polyamine-substituted) polyalkenyl succinimide.
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In this specification, 'hydrocarbyl' means a group containing carbon and
hydrogen atoms that is bonded to the remainder of the molecule via a carbon
atom and
that may include hetero atoms that do not detract from the essentially
hydrocarbon
nature of the group.
DETAILED DESCRIPTION OF THE INVENTION
Features of the invention, applicable where appropriate to various aspects of
the
invention, will now be described in more detail.
(A) QUARTERNARY AMMONIUM SALT
As stated, this is an oil-soluble nitrogen compound effective as a wax anti-
settling
additive in the form of a quatemary ammonium salt of a polycarboxylic acid.
The
nitrogen atom of the ammonium cation carries, for example, four hydrocarbyl
groups.
The salt is for example monomeric.
The quatemary ammonium cation in the compound preferably carries a segment
of the formula NR13R14, where R13 independently represents a hydrocarbyl
group, such
as an alkyl group, containing from 8 to 40 carbon atoms, and R14 independently
represents a hydrocarbyl group, such as an alkyl group, containing up to 40
carbon
atoms. R13 and R14 may be straight chain or branched, and/or may be the same
or
different. Preferably, each of R13 and R14 represents a C12 to C24 straight-
chain alkyl
group.
The quaternary ammonium cation is preferably represented by the
formula NR13R14R2, where R represents an alkyl group having from one to four
carbon atoms such as a methyl, ethyl or propyl group.
Suitably, the segment NR13R14 is derived from a secondary amine such as di-
octadecylamine, di-cocoamine, di-hydrogenated tallow amine and
methylbehenylamine.
The amine may be a mixture such as derived from natural materials, preferably
a
secondary hydrogenated tallow amine, the alkyl groups of which are derived
from
hydrogenated tallow fat composed of approximately 4% C14, 31 % C16 and 59%
C18.
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Examples of suitable polycarboxylic acids and their anhydrides for preparing
the
quaternary ammonium salts include ethylenediamine tetraacetic acid, and
carboxylic
acids based on cyclic skeletons, e.g., cyclohexane-1,2-dicarboxylic acid,
cyclohexene-
1,2-dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid and naphthalene
dicarboxylic
acid, and 1,4-dicarboxylic acids including dialkyl spirobislactones.
Generally, these
acids have 5 to 13 carbon atoms in the cyclic moiety. Preferred acids useful
in the
present invention are benzene dicarboxylic acids, e.g. phthalic acid,
isophthalic acid,
and terephthalic acid. Phthalic acid and its anhydride are particularly
preferred. A
particularly preferred quatemary ammonium salt is represented by the formula
CONR13R14
COO- +NMe2R13R14
where R13 and R14 each independently represent alkyl groups derived from
hydrogenated tallow fat, which compound may, for example, be made by reacting
N,N-
dimethyl-N,N-dihydrogenated tallow ammonium chloride (one mole) with
dihydrogenated tallow amine (one mole), phthalic anhydride (one mole) and
sodium
methoxide (one mole).
(Aref) AMINE SALT
As stated, this is an oil-soluble amine salt of the same polycarboxylic acid
as
described above in respect of (A), the quatemary ammonium salt. It is a polar
nitrogen
compound effective as a wax anti-settling additive but is not a quaternary
ammonium
salt. It may be a primary, secondary or tertiary amine salt.
Such salts may carry the segment of the formula NR13R14 as defined above, but
differ in not being quatemary ammonium salts. They are described in, for
example, US
Patent No. 4,211,534.
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As particular examples, there may be mentioned amide-amine salts formed by
reacting phthalic anhydride (one mole) with dihydrogenated tallow amine (two
moles)
to give an N,N-dialkylammonium salt of a 2-N',N'-dialkylamidobenzoic acid;
reacting
an alkylphenol formaldehyde condensate (APFC) with a dicoco- and
dihydrogenated
tallow amine mixture; and reacting ethylene diamine tetra-acetic acid with
dihydrogenated tallow amine.
In the practice of the present invention, (Aref) is analogous to (A) in that
both
are derived from the same polycarboxylic acid and that the same hydrocarbyl
groups
carried by the nitrogen atom(s) of (Aref) are also carried by nitrogen atoms
of (A).
It will be clear that (Aref) is not a component of the present invention, but
is for
reference purposes in order to defme the scope of the invention.
(B) POLYALKYLENE AMINE DETERGENT
Polyalkylene amines are for example derived from polyalkylenes of greater than
250 mass units, which are themselves preferably derived from C2-Clo alkenes
and more
preferably from butene and/or isobutene. They are prepared by linking
anunonia,
amines, polyamines, alkylamines or alkanolamines to and/or between these
polymers.
A variety of methods can be used to achieve this, for example routes via
chlorination,
hydroformylation, epoxidation and ozonolysis such as are known in the art.
Typical
examples, which are also known in the art, are polyisobutene monoamine
("PIBA") and
polyisobutene-ethylenediamine ("PIB-EDA"). Further examples are described in
EP
244616 and WO 98/28346. The ratio of hydrocarbyl units to amine units may be
1:1 to
2.5:1, preferably 1.2:1 to 1.5:1. A number of acylated, nitrogen-containing
compounds
having a hydrocarbyl substituent of at least 10 carbon atoms and made by
reacting a
carboxylic acid acylating agent, for example an anhydride or ester, with an
amino
compound, are known to those skilled in the art. In such compositions, the
acylating
agent is linked to the amino compound through an imido, amido, amidine or
acyloxy
amnmonium linkage. The hydrocarbyl substituent of at least 10 carbon atoms may
be
found either in the portion of the molecule derived from the carboxylic acid
acylating
agent, or in the portion derived from the amino compound, or in both.
Preferably,
however, it is found in the acylating agent portion. The acylating agent can
vary from
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formic acid and its acylating derivatives to acylating agents having high
molecular
weight hydrocarbyl substituents of up to 50, 75, 100 or 200 carbon atoms. The
amino
compounds can vary from ammonia itself to amines having hydrocarbyl
substituents of
up to about 30 carbon atoms.
Polyalkylene amines are normally regarded as metal-free.
A preferred class of detergent may be those made by reacting an acylating
agent
having a hydrocarbyl substituent of at least 10 carbon atoms and a nitrogen
compound
characterized by the presence of at least one -NH- group. Typically, the
acylating agent
is a mono- or polycarboxylic acid (or reactive equivalent thereof), such as a
substituted
suceinic or propionic acid, and the amino compound is a polyamine or mixture
of
polyamines, most typically, a mixture of ethylene polyamines. The amine also
may be
a hydroxyalkyl-substituted polyamine. The hydrocarbyl substituent in such
acylating
agents preferably contains an average of at least 30 or 50 and up to 200
carbon atoms.
Illustrative of hydrocarbyl substituent groups containing at least 10 carbon
atoms are n-decyl, n-dodecyl, tetrapropenyl, n-octadecyl, oleyl,
chlorooctadecyl and
triicontanyl. Generally, the hydrocarbyl substituents are made from homo- or
interpolymers (e.g. copolymers such as terpolymers) of mono- and di-olefins
having 2
to 10 carbon atoms, such as ethylene, propylene, 1-butene, isobutene,
butadiene,
isoprene, 1-hexene and 1-octene. Typically, these olefins are 1-monoolefins.
This
substituent can. also be derived from halogenated (e.g. chlorinated or
brominated)
analogues of such homo- or interpolymers.
The hydrocarbyl substituents are predominantly saturated. The hydrocarbyl
substituents are also predominantly aliphatic in nature, that is, they contain
no more
than one non-aliphatic moiety (cycloalkyl, cycloalkenyl or aromatic) group of
6 or less
carbon atoms for every 10 carbon atoms in the substituent. Usually, however,
the
substituents contain no more than one such non-aliphatic group for every 50
carbon
atoms, and in many cases they contain no such non-aliphatic groups at all,
that is, the
typical substituents are purely aliphatic. Typically, these purely aliphatic
substituents
are alkyl or alkenyl groups.
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A preferred source of the substituents are poly(isobutene)'s obtained by
polymerization of a C4 refinery stream having a butene content of 35 to 75
weight per
cent and an isobutene content of 30 to 60 weight per cent in the presence of a
Lewis
acid catalyst such as aluminium trichloride or boron trifluoride. These
polybutenes
predominantly contain monomer repeating units of the configuration -C(CH3)2CH2-
.
The hydrocarbyl substituent is attached to the succinic acid moiety or
derivative
thereof via conventional means, for example the reaction between maleic
anhydride and
an unsaturated substituent precursor such as a polyalkene, as described for
example in
EP-B-0 451 380.
One procedure for preparing the substituted succinic acylating agents involves
first chlorinating the polyalkene until there is an average of at least one
chloro group for
each molecule of polyalkene. Chlorination involves contacting the polyalkene
with
chlorine gas until the desired amount of chlorine is incorporated into the
chlorinated
polyalkene. Chlorination is generally carried out at a temperature of 75 to
125 C. If
desired, a diluent can be used in the chlorination procedure. Suitable
diluents for this
purpose include poly- and perchlorinated and/or fluorinated alkanes and
benzenes.
The second step in the procedure is to react the chlorinated polyalkene with
the
maleic reactant at a temperature usually within the range of 100 to 200 C. The
mole
ratio of chlorinated polyalkene to maleic reactant is usually 1:1. However, a
stoichiometric excess of maleic reactant can be used, for example, a mole
ratio of 1:2.
If an average of more than one chloro group per molecule of polyalkene is
introduced
during the chlorination step, then more than one mole of maleic reactant can
react per
molecule of chlorinated polyalkene. It is normally desirable to provide an
excess of
maleic reactant, for example, an excess of 5 to 50, for example 25,% by
weight.
Unreacted excess maleic reactant may be stripped from the reaction product,
usually
under vacuum.
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Another procedure for preparing substituted succinic acid acylating agents
utilizes a process described in U.S. Patent No. 3,912,764 and U.K. Patent No.
1,440,219.
According to that process, the polyalkene and the maleic reactant are first
reacted by
heating them together in a direct alkylation procedure. When the direct
alkylation step
is completed, chlorine is introduced into the reaction mixture to promote
reaction of the
remaining unreacted maleic reactants. According to these patent
specifications, 0.3 to 2
or more moles of maleic anhydride are used in the reaction for each mole of
polyalkene.
The direct alkylation step is conducted at temperatures of 180 to 250 C.
During the
chlorine-introducing stage, a temperature of 160 to 225 C is employed.
The attachment of the hydrocarbyl substituent to the succinic moiety may
alternatively be achieved via the thermally-driven 'ene' reaction in the
absence of
chlorine. Use of such a material as the acylating agent leads to products
having
particular advantages, for example, to chlorine-free products having excellent
detergency and lubricity properties. In such products, the reactant is
preferably formed
from a polyalkene having at least 30, preferably 50 or more such as 75, % of
residual
unsaturation in the form of terminal, e.g. vinylidene, double bonds.
Suitable polyalkylene amines are those comprising amino nitrogens linked by
alkylene bridges, which amino nitrogens may be primary, secondary and/or
tertiary.
The polyamines may be straight chain, wherein all the amino groups are primary
or
secondary, or may contain cyclic or branched regions or both, in which case
tertiary
amino groups may also be present. The alkylene groups are preferably ethylene
or
propylene groups, most preferably ethylene. Such materials may be prepared
from the
polymerization of lower alkylene diamines such as ethylene diamine, a mixture
of
polyamines being obtained, or via the reaction of dichloroethane and ammonia.
Specific examples of polyalkylene polyamines (1) are ethylene diamine,
tetra(ethylene)pentamine, tri-(trimethylene)tetramine, and 1,2-propylene
diamine.
Specific examples of hydroxyalkyl-substituted polyamines include N-(2-
hydroxyethyl)
ethylene diamine, N,N-bis-(2-hydroxyethyl) ethylene diamine and N-(3-
hydroxybutyl)
tetramethylene diamine. Specific examples of heterocyclic-substituted
polyamines (2)
are N-2-aminoethyl piperazine, N-2 and N-3 amino propyl morpholine, N-3-
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(dimethylamino) propyl piperazine, 2-heptyl-3-(2-aminopropyl) imidazoline, 1,4-
bis (2-
aminoethyl) piperazine, 1-(2-hydroxy ethyl) piperazine and 2-heptadecyl-l-(2-
hydroxyethyl)-imidazoline. Specific examples of aromatic polyamines (3) are
isomeric
phenylene diamines and isomeric naphthalene diamines.
Many patent specifications describe suitable polyalkylene amine detergents
including US Patents 3 172 892; 3 219 666; 3 272 746; 3 310 492; 3 341 542;
3 444170; 3 455 831; 3 455 832; 3 576 743; 3 630 904; 3 632 511; 3 804 763 and
4 234 435, and including EP 0 336 664 and EP 0 263 703. A typical and
preferred
detergent of this class, is that made by reacting a poly(isobutylene)-
substituted succinic
anhydride acylating agent (e.g. anhydride, acid or ester.) wherein the
poly(isobutene)
substituent has between 50 to 200 carbon atoms with a mixture of ethylene
polyamines
having 3 to 10 amino nitrogen atoms per ethylene polyamine and 1 to 6 ethylene
groups.
The polyalkylene amine may be defined by the average number of nitrogen
atoms per molecule of the component, which may preferably be in the range of 4
to 8.5,
more preferably 6.8 to 8, especially 6.8 to 7.5, nitrogen atoms per molecule.
Also suitable are materials made from amine mixtures comprising polyamines
having seven and eight, and optionally nine, nitrogen atoms per molecule (so-
called
'heavy' polyamines). Preferably, the polyamine mixture comprises at least 45,
and
preferably 50, % by weight of polyamines having seven nitrogen atoms per
molecule,
based on the total weight of polyamines. In addition to polyamine mixtures,
single
species may also be used, for example tetraethylene pentamine (TEPA) and
triethylene
tetramine (TETA).
Preferred polyalkylene amine detergents are those made by reacting a
poly(isobutene)-substituted succinic anhydride acylating agent with mixtures
of
ethylene polyamines as hereinbefore described, wherein the polyisobutene has a
Mn of
400-2500, preferably 700-400, such as 950. Generally, they may be described as
polyalkenyl succinimides (such as polybutenyl succimides, preferably
polyisobutenyl
succinimides) or as N-(polyamine-substituted) polyalkenyl succinimides.
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THE FUEL OIL
The fuel oil is a petroleum-based fuel oil in the form of a middle distillate
fuel
oil, generally boiling within the range of from 110 to 500, e.g. 150 to 400,
C.
The invention is applicable to middle distillate fuel oils of all types,
including
broad-boiling distillates, i.e., those having a 90%-20% boiling temperature
difference,
as measured in accordance with ASTM D-86, of 50 C or more.
The fuel oil may comprise atmospheric distillate or vacuum distillate, cracked
gas oil, or a blend in any proportion of straight-run and thennally and/or
catalytically
cracked distillates. The most common petroleum distillate fuels are kerosene,
jet fuels,
diesel fuels, heating oils and heavy fuel oils. The heating oil may be a
straight
atmospheric distillate, or may also contain vacuum gas oil or cracked gas oil
or both.
The fuels may also contain major or minor amounts of components derived from
the
Fischer-Tropsch process. Fischer-Tropsch fuels, also known as FT fuels,
include those
that are described as gas-to-liquid fuels, coal and/or biomass conversion
fuels. To make
such fuels, syngas (CO + H2) is first generated and then converted to normal
paraffins
and olefins by a Fischer-Tropsch process. The normal paraffins may then be
modified
by processes such as catalytic cracking/reforming or isomerisation,
hydrocracking and
hydroisomerisation to yield a variety of hydrocarbons such as iso-paraffins,
cyclo-
paraffins and aromatic compounds. The resulting FT fuel can be used as such or
in
combination with other fuel components and fuel types such as those mentioned
in this
specification. The above-mentioned low temperature flow problem is most
usually
encountered with diesel fuels and with heating oils. The invention is also
applicable to
fuel oils containing fatty acid methyl esters derived from vegetable oils, for
example,
rapeseed methyl ester, either used alone or in admixture with a petroleum
distillate oil.
The fuel oil is preferably a low sulphur-content fuel oil. Typically, the
sulphur
content of the fuel oil is less than 500ppm (parts per million) by weight.
Preferably, the
sulphur content of the fuel is less than 100, for example less than 50, ppm.
Fuel oils
with even lower sulphur contents, for example less than 20ppm or less than
10ppm are
also suitable.
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TREAT RATES
The amounts of each component present in the fuel oil depend on the nature of
the species used, the properties of the fuel oil and the low temperature
performance
required. As discussed above, the present invention is based on the
observation of a
negative impact on the low temperature behaviour of the wax anti-settling
additive
when present in premium diesel fuels which contain relatively high levels of
polyamine
detergent.
Typically, the amount of (B), at least one polyalkylene amine detergent, in
the
fuel oil composition is in excess of 50ppm by weight based on the weight of
the fuel oil,
for example in excess of 75 or 100, ppm by weight. Some premium diesel fuels
may
contain up to 500 ppm by weight of polyalkylene amine detergent. This can be
compared with a treat rate of around 10 to 75 ppm for more conventional, non-
premium
diesel fuels.
The amount of (A), at least one polar nitrogen compound in the form of the
quaternary ammonium compound effective as a wax anti-settling additive, is
typically
in the range of 10 to 500, preferably 20 to 250, more preferably 20 to 150,
ppm by
weight based on the weight of the fuel oil. Alternatively, the preferments may
be 10 to
200, more preferably 10 to 100.
OTHER ADDITIVES
It i$ commonplace in the art to use polar nitrogen compounds effective as a
wax
anti-settling additives in combination with other additional cold-flow
improving
additives. Suitable materials will be well known to those skilled in the art
and include
for example, ethylene-unsaturated ester copolymers such as ethylene:vinyl
acetate
copolymers and similar polymers. The present invention contemplates the
addition of
such additional cold-flow improving additives, their application in terms of
treat rate
also being well-known to those skilled in the art. In an embodiment of all
aspects of the
invention, the fuel oil further comprises an ethylene-unsaturated ester
copolymer.
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EXAMPLES OF THE INVENTION
The invention will now be described in the examples which are not intended to
limit the scope of the claims hereof.
CONSTITUENTS
The following were used:
WASA (Aref): a monomeric polar nitrogen compound effective as a wax anti-
settling additive in the form of an N,N-dialkylammonium salt of 2-N',N'-
dialkylamidobenzoic acid, made by reacting phthalic anhydride (one mole) and
di(hydrogenated tallow) amine (two moles).
WASA (A): a monomeric polar nitrogen compound effective as a wax anti-
settling additive in the form of an N,N-dimethyldi-dihydrogenated tallow
ammonium
salt of 2-(N',N'-dihydrogenated tallow amido)benzoic acid, made by reacting
N,N-
dimethyl-N,N-dihydrogenated ammonium chloride (one mole) with dihydrogenated
tallow amine (one mole), phthalic anhydride (one mole) and sodium methoxide
(one
mole). Sodium chloride (a by-product) was separated by washing with water and
removing the aqueous solution.
DETERGENT (B): a succinimide detergent made by reacting polyisobutene-
substituted succinic anhydride, in which the polyisobutene group has a
molecular
weight of about 1000, with a poly-ethyleneamine mixture predominating in
species
having at least seven nitrogen atoms per molecule.
FUELS: the fuel used was a middle-distillate diesel fuel, Fuel X:
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Fuel X is characterised by
D86 Distillation IBP 199 C
20% 231 C
90% 319 C
FBP 352 C
Cloud Point -6 C
CFPP -13 C
TESTS
Additives (A), (Aref) and (B) were blended into Fuel X in proportions
indicated
below to give middle distillate fuel oil compositions. The compositions also
contained
additives routinely used in diesel fuels such as ethylene unsaturated ester
copolymers
(EVE), dialkyl fumarate vinyl acetate copolymers (FVA), polyethylene glycol
esters
(PEGE) and alkyl phenol formaldehyde condensates (APFC). Such additives will
be
referred to below by the above-indicated abbreviations.
All additive proportions below are expressed as ppm of active ingredient (i.e.
ingredient which is not solvent or carrier) by mass based on the mass of the
fuel.
Low temperature properties of the compositions were measured as follows:
The Aral Short Sediment Test
The Aral Short Sediment Test (ASST) is a measurement of the propensity of the
wax content of a fuel oil to settle and thus a determination of the
effectiveness of a wax
anti-settling additive. This test was developed by the German oil company Aral
and is
widely accepted throughout'Europe. The ASST metric is the "OCP", delta Cloud
Point,
which is measured as follows: the Cloud Point (CP) of a base fuel oil is
measured. The
wax anti-settling additive combination under study is added to the base fuel
and the
sample is stored a temperature 7 C below the measured CP, namely, usually for
German winter diesel fuels, -13 C, for 16 hours. The amount of wax that is
judged by
f
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eye to have settled is noted. The bottom 20% of the fuel is then taken and the
CP of this
sample is measured and compared to that of the base fuel. ACP is the
difference [CP of
base fuel] minus [CP of additized fuel]; thus, the greater the OCP, the
greater the degree
of wax settling. A small value of ACP, preferably around zero, indicates good
wax
dispersion.
Cold Filter Plunin2 Point ("CFPP")
CFPP is a standard industry test to evaluate the ability of a fuel oil sample
to
flow through a filter at reduced temperature. The test, which is carried out
by the
procedure described in detail in "Jn. Of the Institute of Petroleum", vol. 52,
No. 510
(1996), p 173-285, is designed to correlate with the cold flow of a middle
distillate fuel
oil in automotive diesels. In brief, a sample of the oil to be tested (40 cm3)
is cooled in
a bath which is maintained at about -34 C to give an average cooling rate of
about
1 C/min. Periodically (at each one degree centigrade starting from above the
cloud
point), the oil is tested for its ability to flow through a fine screen in a
prescribed time
period using a test device which is a pipette to whose lower end is attached
an inverted
funnel which is positioned below the surface of the oil to be tested.
Stretched across the
mouth of the funnel is a 350 mesh screen having an area defmed by a 12 mm
diameter.
The periodic tests are initiated by applying a vacuum to the upper end of the
pipette
whereby oil is drawn through the screen up into the pipette to a mark
indicating 20 cm3
of oil. After each successful passage, the oil is returned inunediately to the
CFPP tube.
The test is repeated with each one degree drop in temperature until the oil
fails to fill the
pipette within 60 seconds, the temperature at which failure occurs being
reported as the
CFPP temperature.
RESULTS
Results of test carried out on fuel oil compositions based on Fuel X are set
out in
Table 1 below.
In a first set of tests, three groups of fuel oil compositions were used at
respective EVE concentrations of 220, 290 and 365 ppm. Each of those three
groups
included oils with respective detergent, (B), concentrations of 0, 50 and 100
ppm, and
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each of those oils included oils containing 100 ppm of the reference WASA,
(Aref), or
of the WASA, (A), of the invention. Thus, eighteen oils based on Fuel X were
tested.
Table 1
EVE (ppm) Detergent (B) WASA (Aref) WASA (A)
(PPm)
220 0 0.1 0.4
220 50 5.8 0.6
220 100 4.5 0.9
290 0 0.1 0.1
290 50 6 0.5
290 100 4.4 1.1
365 0 0.5 0.4
365 50 4.4 0.8
365 100 3.8 1.2
The results, shown in the right-hand columns, are of ACP. A small value such
as around zero indicates a good performance, whereas a larger value, e.g. 4 to
6 degC,
indicates a poor performance. They demonstrate that, when detergent (B) is
present,
the wax anti-settling performance of reference WASA (Aref) is almost
completely lost.
In contrast, when WASA (A) of the invention is used, its wax anti-settling
performance
is substantially retained in the presence of detergent (B).
Results of a second set of tests carried out on fuel oil compositions based on
Fuel X are set out in Table 2 below. All compositions based on Fuel X
contained a
didodecyl fumarate: vinyl acetate copolymer (25 ppm) and an APFC (25 ppm),
both
being known cold flow improver additives.
Three groups of fuel oil compositions were used at respective EVE
concentrations of 220, 290 and 365 ppm.
Each of these three groups included oils with either 0 or 100 ppm detergent,
(B),
and with either 0 or 20 ppm of a polyethylene glycol ester ("PEGE") cold flow
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improver. Each oil contained 50 ppm of the reference WASA, (Aref), or of the
WASA,
(A), of the invention. Thus, twenty-four oils based on Fuel X were tested.
Table 2
EVE (ppm) PEGE (ppm) Detergent (B) WASA (Aref) WASA (A)
(ppm)
220 0 0 -19.5 -19
220 0 100 -18.5 -20
220 20 0 -25.25 -18.5
220 20 100 =18 -20
290 0 0 -24 -19.7
290 0 100 -18 -24
290 20 0 -25.75 -22
290 20 100 -19.5 -27
365 0 0 -26.3 -27
365 0 100 -19.5 -28
365 20 0 -26.5 -25.3
365 20 100 -22.5 -26
The results, shown in the two adjacent right-hand columns, are of CFPP in C.
They demonstrate that, in the absence of detergent, (B), the CFPP of oils
containing the
reference WASA, (Aref), is either better than or comparable to the CFPP of
oils
containing the WASA of the invention, (A). However; they also demonstrate
that, in
the presence of detergent, (B), the CFPP advantage is lost and that there is a
further
CFPP advantage in including (A) in place of (Aref).
