Note: Descriptions are shown in the official language in which they were submitted.
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Improvements in fuel oils
This invention relates to fuel oil compositions with improved low-temperature
properties.
Fuel oils derived from petroleum sources contain n- alkanes that at low
temperatures, 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 oil 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 that
form 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 waxes to adopt an acicular habit, the
resulting needles being
more likely to pass through a filter, or form a porous layer of crystals on
the filter, than are
platelets. Other additives may also have the effect of retaining the wax
crystals in suspension in
the fuel, reducing settling and thus also assisting in the prevention of
blockages. Additives of
these types are commonly referred to as cold-flow additives.
Recent years have seen an increase in the use of alternatives to petroleum
materials as
sources for fuel oils. Bio-diesels, which are commonly the methyl esters of
natural oils such as
vegetable oils, are now used as blend components in many commercial diesel
fuels. However,
because bio-diesels are produced from natural materials, they are inherently
variable in terms of
their precise composition and their physical and chemical properties. As an
alternative to using
natural oils to produce methyl esters for use as fuels, it is known in the art
to hydrotreat the oils to
provide paraffinic mixtures and employ these products as fuels or as blend
components to be
combined with conventional diesel fuels. The products of hydrotreating are n-
alkanes and as such,
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are essentially indistinguishable from the n-alkanes normally found in
petroleum-derived diesel
fuels. Hydrotreated vegetable oils (HVO) tend to be more uniform in
composition and properties
and have fewer impurities than methyl ester bio-diesels. The process of
hydrotreating also allows
greater control over the products obtained. It would thus be desirable to be
able to use HVO as a
blend component for petroleum-derived diesel fuels.
However HVOs tend to have a well-defined and narrow n-alkane distribution. The
addition of such a blend component to a petroleum-derived diesel fuel gives
rise to a `spike' in
the overall n-alkane distribution of a diesel-HVO fuel blend. This `spike'
alters the n-alkane
distribution in the region which is most crucial for low-temperature
performance. In many cases,
a petroleum diesel fuel which could otherwise be easily treated with
conventional cold-flow
additives will be rendered essentially untreatable by the addition of a
significant amount of HVO.
This places a practical restriction on the use of HVO as a blend component for
diesel fuels,
particularly for use in regions where low temperature performance is
important.
As noted below, oils suitable for hydrotreating may be obtained from sources
other than
vegetable oils. Oils and fats from animal and fish sources are also suitable.
The term 'HVO' is
used in this specification for convenience and encompasses hydrotreated oils
obtained from any
suitable source and thus should not be read as limited to those oils obtained
only from vegetable
sources.
The present invention is based on the discovery that specific combinations of
polymeric
cold-flow additives are effective to improve the low temperature properties of
blends of
petroleum-derived diesel fuel and HVO.
In accordance with a first aspect, the present invention provides a fuel oil
composition
comprising a fuel oil blend, at least one ethylene-vinyl ester polymer and at
least one
polyalkylmethacrylate polymer, wherein the fuel oil blend comprises a middle-
distillate fuel oil
and a hydrotreated vegetable, animal or fish oil, and wherein the amount of
hydrotreated
vegetable, animal or fish oil in the fuel oil blend is sufficient to provide
the blend with an
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increase in the C15 to C20 n-alkane distribution of at least 3% by weight over
the C15 to C20 n-
alkane distribution of the middle-distillate alone.
In accordance with a second aspect, the present invention provides method of
improving
the low temperature properties of a blend of a middle-distillate fuel oil and
a hydrotreated
vegetable, animal or fish oil, wherein the amount of hydrotreated vegetable,
animal or fish oil in
the blend is sufficient to provide the blend with an increase in the C15 to
C20 n-alkane distribution
of at least 3% by weight over the C15 to C20 n-alkane distribution of the
middle-distillate alone,
the method comprising adding to the blend at least one ethylene-vinyl ester
polymer and at least
one polyalkylmethacrylate polymer.
In accordance with a third aspect, the present invention provides the use of
at least one
ethylene-vinyl ester polymer and at least one polyalkylmethacrylate polymer to
improve the low
temperature properties of a blend of a middle-distillate fuel oil and a
hydrotreated vegetable,
animal or fish oil, wherein the amount of hydrotreated vegetable, animal or
fish oil in the blend
is sufficient to provide the blend with an increase in the C15 to C20 n-alkane
distribution of at least
3% by weight over the C15 to C20 n-alkane distribution of the middle-
distillate alone.
With regard to the second and third aspects, preferably the improvement in low
temperature properties of the blend of a middle-distillate fuel oil and a
hydrotreated vegetable,
animal or fish oil is as determined by CFPP measurement.
In all aspects of the invention, the at least one ethylene-vinyl ester polymer
and the at
least one polyalkylmethacrylate polymer may be added separately to the fuel
oil blend, or added
to the blend together as an additive composition. It is also within the scope
of the present
invention to add both of the polymers to the middle-distillate fuel oil and
then blend this mixture
with the hydrotreated vegetable, animal or fish oil, or to add both of the
polymers to the
hydrotreated vegetable, animal or fish oil and then blend this mixture with
the middle-distillate
fuel oil. Finally, one of the polymers may be added to one of the fuel blend
components and the
other polymer added to the other fuel blend component, the final fuel oil
composition being the
result of combining the two mixtures so obtained.
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It is noteworthy that when used alone, neither the ethylene-vinyl ester
polymer nor the
polyalkylmethacrylate polymer were found to be effective to improve the low
temperature
properties of the middle-distillate fuel oil/HVO blend. Mixtures of different
ethylene-vinyl ester
polymers were similarly not effective. Acceptable performance was only found
for the specific
combination of additives.
The various features of the invention, which are applicable to all aspects
will now be
described in more detail.
The fuel oil blend
The fuel oil blend comprises a middle-distillate fuel oil and a hydrotreated
vegetable,
animal or fish oil.
Middle-distillate fuel oils generally boil within the range of from 110 C to
500 C, e.g.
150 C to 400 C. The present invention is applicable to middle-distillate fuel
oils of all types,
including the 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
middle-distillate
fuel oil may comprise atmospheric distillate or vacuum distillate, cracked gas
oil, or a blend in
any proportion of straight run and thermally 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 middle-distillate fuel oil is preferably a low
sulphur content fuel
oil. Typically, the sulphur content of the fuel oil will be less than 500ppm
(parts per million by
weight). Preferably, the sulphur content of the fuel will be less than 100ppm,
for example, less
than 50ppm. Fuel oils with even lower sulphur contents, for example less that
20ppm or less than
10ppm are also suitable. Suitable are middle-distillate diesel fuels meeting
the EN 590 or ASTM
D 975 standard specifications.
The hydrotreated vegetable, animal or fish oil may be produced in a known
manner from
natural raw materials containing fatty acids, fatty acid esters (e.g. tri-
glyceride oils) and mixtures
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of these. Suitable vegetable-based raw materials are rapeseed oil, sunflower
oil, soyabean oil,
hemp oil, olive oil, palm oil, coconut oil, linseed oil, mustard oil, peanut
oil, castor oil and the
like. Included within the scope of vegetable-based are oils obtained from
wood, e.g. tall oil.
Animal-based fats and oils include tallow and lard. Also suitable are used and
recycled fats and
5 oils from the food industry.
The hydrotreated vegetable, animal or fish oil may be obtained from the
natural raw
materials by hydrogenating and decomposing the fatty acids and/or fatty acid
esters to produce
predominantly n-paraffins having between 12 and 24 carbon atoms. The patent
literature
describes several examples of processes to produce hydrotreated vegetable,
animal or fish oils
suitable for use in the present invention. See for example US 4,992,605, US
5,705,722,
FR 2 607 803, W02004/022674 Al and W02007/068795 Al.
The fuel oil blend preferably contains a major proportion of the middle-
distillate fuel oil
and a minor proportion of the HVO. In all aspects of the invention, the amount
of HVO contained
in the fuel oil blend is an amount which is sufficient to provide the fuel oil
blend with an increase
(spike) in the C15 to C20 n-alkane distribution of at least 3% by weight over
the C15 to C20
n-alkane distribution of the middle-distillate alone. The actual amount of HVO
required to obtain
a 3% by weight increase will vary with the isomerisation level of the HVO and
the n-alkane
distribution of the middle-distillate fuel oil.
Preferably, the amount of HVO contained in the fuel oil blend is an amount
which is
sufficient to provide the fuel oil blend with an increase (spike) in the C15
to C20 n-alkane
distribution of at least 3.5% by weight, more preferably at least 4% by
weight, over the C15 to C20
n-alkane distribution of the middle-distillate alone.
Preferably, the amount of HVO contained in the fuel oil blend is not greater
than the
amount which is sufficient to provide the fuel oil blend with an increase
(spike) in the C15 to C20
n-alkane distribution of more than 25% by weight, over the C15 to C20 n-alkane
distribution of the
middle-distillate alone.
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Determination of the extent of the `spike' in the C15 to C20 n-alkane
distribution is simply
a matter of subtracting the appropriate part of the n-alkane distribution of
the middle-distillate
fuel oil from that of the blend. Techniques for determining the n-alkane
distributions of fuel oils
will be known to those skilled in the art. Gas chromatography is a suitable
method.
Typically the fuel oil blend will comprise from 50 to 95%, preferably from 65
to 95% by
weight of the middle-distillate and from 5 to 50%, preferably from 5 to 35% by
weight of HVO.
Ethylene-vinyl ester polymer
In an embodiment, the ethylene-vinyl ester polymer comprises a copolymer of
ethylene
and a vinyl ester, wherein the copolymer has a vinyl ester content of between
5 and 25 mole %,
preferably between 10 and 20 mole%.
Preferably the ethylene-vinyl ester polymer has a number average molecular
weight (Mn)
as measured by GPC with reference to polystyrene standards of between 2,000
and 10,000, more
preferably between 3,000 and 9,000, for example between 3,000 and 7,000.
Preferably, the vinyl ester corresponds to formula (I)
CH2 CH OCOR (I)
where R is a C1 to C30 alkyl group, preferably a C, to C16 alkyl group, more
preferably a
C1 to C12 alkyl group. The alkyl group may optionally be substituted by one or
more hydroxyl
groups. Group R may be linear or branched. In a preferred embodiment where R
is branched, R is
a branched alkyl group or a neoalkyl group having from 7 to 11 carbon atoms,
preferably 8, 9 or
10 carbon atoms. Suitable are vinyl esters derived from secondary or tertiary
carboxylic acids
with a branching point in the alpha-position to the carbonyl group.
Preferably the vinyl ester is chosen from the group of vinyl acetate, vinyl
propionate,
vinyl butyrate, vinyl isobutyrate, vinyl hexanoate, vinyl heptanoate, vinyl
octanoate, vinyl
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pivalate, vinyl 2-ethylhexanoate, vinyl laurate, vinyl stearate, vinyl
neodecanoate, vinyl
neononanoate and vinyl undecanoate. Vinyl acetate is most preferred.
In a further embodiment, the ethylene-vinyl ester polymer comprises a
terpolymer of
ethylene, vinyl acetate and a further vinyl ester corresponding to formula (I)
which is not vinyl
acetate. Preferably this terpolymer comprises a terpolymer of ethylene, vinyl
acetate and a
branched-chain ester chosen from the group of vinyl 2-ethylhexanoate, vinyl
neononanoate, vinyl
neodecanoate and vinyl neoundecanoate.
Preferred are terpolymers which apart from ethylene, contain 1 to 15 mole %,
preferably 2
to 10 mole% of vinyl acetate, and 0.1 to 25 mole %, preferably 5 to 20 mole %
of the further
vinyl ester corresponding to formula (I) which is not vinyl acetate,
preferably a branched-chain
ester, more preferably a branched-chain ester chosen from the group of vinyl 2-
ethylhexanoate,
vinyl neononanoate, vinyl neodecanoate and vinyl neoundecanoate. The total
ester content of the
polymers is preferably 5 to 30 mole%, more preferably 10 to 20 mole %, for
example from 12 to
18 mole%.
Preferably the terpolymers have a number average molecular weight (Mn) as
measured by
GPC with reference to polystyrene standards of between 2,500 and 12,000, more
preferably
between 3,000 and 9,000, for example between 4,000 and 7,000.
The polymers may be made from ethylene and vinyl ester monomers by processes
known
in the art.
Pol alkylmethacr, 1~ ate polymer
The polyalkylmethacrylate polymer is preferably formed or obtainable from
monomers
corresponding to formula (II)
CH3
CH2 C COOR1 (II)
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wherein R' is a C4 to C16 alkyl group, preferably a C8 to C16 alkyl group,
more preferably
a C12 to C16 alkyl group. Single monomers where each R1 group is the same or
mixtures of
monomers with different R1 groups within the given ranges are suitable.
Preferred are polymers
where the monomers used are exclusively or predominantly those having as R1 a
C14 alkyl group
(tetradecyl), or a C12 alkyl group (dodecyl).
Preferably, the at least one polyalkylmethacrylate polymer has a number
average
molecular weight in the range from 1,500 to 6,000, more preferably from 2,000
to 4,000, as
measured by GPC with reference to polystyrene standards.
Methods for the production of the polyalkylmethacrylate polymer will be known
to those
skilled in the art. Free-radical polymerisation as described in US 4,694,054
is one suitable
method.
Preferably the combined total amount of ethylene-vinyl ester polymer and
polyalkylmethacrylate polymer in the fuel oil composition is in the range from
100 to 5,000 ppm
by weight, based on the weight of the fuel oil blend. More preferably, the
combined total amount
of ethylene-vinyl ester polymer and polyalkylmethacrylate polymer in the fuel
oil composition is
in the range from 200 to 3,000 ppm by weight, for example 500 to 2,500 ppm by
weight, based
on the weight of the fuel oil blend.
Preferably the weight ratio of ethylene-vinyl ester polymer to
polyalkylmethacrylate
polymer in the fuel oil composition is in the range from 1:8 to 8:1, more
preferably from 1:5 to
5:1, for example from 1:2 to 2:1.
Co-additives
The fuel oil composition may further contain one or more co-additives. These
additives
may be additional cold-flow additives which may further enhance the low
temperature properties
of the fuel oil composition and/or they may be co-additives used to provide
the fuel oil
composition with additional advantageous properties.
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A preferred additional cold-flow additive is an oil-soluble hydrogenated block
diene
polymer. Preferably this block diene polymer comprises at least one
crystallisable block,
obtainable by end-to-end polymerisation of a linear diene, and at least one
non-crystallisable
block, the non-crystallisable block being obtainable by 1,2-configuration
polymerisation of a
linear diene, by polymerisation of a branched diene, or by a mixture of such
polyinerisations.
Preferably, the block copolymer before hydrogenation comprises units derived
from
butadiene only, or from butadiene and at least one comonomer of formula (III)
CH2 CR2-CR3=CH2 (III)
wherein R2 represents a C1 to C8 alkyl group and R3 represents hydrogen or R2.
Preferably, the total number of carbon atoms in the comonomer of formula (III)
is 5 to 8. A
preferred comonomer of formula (III) is isoprene. Preferably, the block
copolymer contains at
least 10% by weight of units derived from butadiene.
In general, the crystallisable block or blocks will be the hydrogenation
product of the unit
resulting from predominantly 1,4 or end-to-end polymerisation of butadiene,
while the non-
crystallisable block or blocks will be the hydrogenation product of the unit
resulting from 1,2
polymerisation of butadiene or from 1,4 polymerisation of an alkyl-substituted
butadiene.
In a preferred embodiment of all aspects of the present invention, the fuel
oil composition
comprises, in addition to the at least one ethylene-vinyl ester polymer and
the at least one
polymethacrylate polymer, an oil-soluble hydrogenated block diene polymer as
described herein.
Preferably, the amount of oil-soluble hydrogenated block diene polymer is in
the range of from
1% to 20% by weight of combined total amount of ethylene-vinyl ester polymer
and
polyalkylmethacrylate polymer, more preferably in the range of from 1% to 15%,
for example
5% to 15%.
Other additional cold-flow additives include comb polymers such as fumarate-
vinyl
acetate copolymers; hydrocarbon polymers such as ethylene a-olefin copolymers,
and similar
CA 02774619 2012-04-20
polymers. Such species are known in the art. Also suitable are additives known
in the art as wax
anti-settling additives (WASA) which are usually oil-soluble polar nitrogen
compounds. Also
suitable are condensate species such as alkyl-phenol formaldehyde condensates
as described for
example in EP 0 857 776 B1 and EP-A-1 767 610 , or hydroxy-benzoate
formaldehyde
5 condensates as described in EP-A-1 482 024.
Types of co-additives useful to provide the fuel oil composition with
additional
advantageous properties will be known in the art. These include lubricity
additives, anti-oxidants,
electrical conductivity improving additives, metal deactivators, demulsifiers
and the like. When
10 used, these additional additives are used in conventional amounts.
The invention will now be described by way of example only.
The additive components used are detailed in Table 1 below.
Component Type Description
A ethylene vinyl acetate 12 mol% vinyl acetate, Mn 4600
B ethylene vinyl acetate/ 1.7 mol% vinyl acetate; 15.5 mol% vinyl 2-
vinyl 2-eth yl hexanoate eth lhexanoate; Mn 6300
C ethylene vinyl acetate/ 3.5 mol% vinyl acetate; 11.2 mol% vinyl 2-
vinyl 2-eth yl hexanoate eth lhexanoate; Mn 5770
D pol alkylmethacr late Tetradecylmethacrylate, Mn 2600
E hydrogenated block Butadiene-derived
diene
Table I
These additive components were added in various amounts to a blend of a low
sulphur-
content diesel fuel and HVO. Amounts are expressed in parts per million (wppm)
by weight,
based on the weight of the fuel blend. The effect of the addition of HVO to
the diesel fuel was to
increase the C15 - C20 n-alkane distribution of the fuel by 4% compared to the
diesel fuel alone.
The amount of HVO added to the diesel fuel was 30% by weight, based on the
weight of the
diesel fuel.
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CFPP measurements were performed. CFPP (Cold Filter Plugging Point) is the
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), pp 173-285, is designed to
correlate with the
cold flow of a middle distillate 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 linear
cooling at 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 defined 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 em3 of oil. After each successful passage, the
oil is returned
immediately 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. The base CFPP of the diesel fuel/HVO
blend was -19 C.
Results are given in Table 2 below.
Example component amount component amount component amount CFPP
/wppm /wppm /wppm / C
1 A 1200 -21.0
2 C 1366 -20.5
3 B 1500 -21.5
4 A 712 C 712 -21.0
5 A 520 B 650 E 130 -22.0
6 A 712 B 712 -21.5
7 D 1920 -23.0
8 A 300 D 1440 -26.0
9 A 600 D 960 -26.0
10 A 900 D 480 -29.0
11 B 630 D 605 E 140 -28.0
Table 2
Examples not according to the present invention (Examples 1 to 7 inclusive)
had little
effect on the CFPP of the diesel fuel/HVO blend. By comparison, examples of
the invention
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(Examples 8 to 11 inclusive) were able to depress the CFPP of the fuel blend
to a significant
degree.
