Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ALTERING PROPERTIES OF FUEL COMPOSITIONS
The present invention relates to a method for
increasing the cetane number of a diesel fuel
composition.
The cetane number of a fuel or fuel composition is a
measure of its ease of ignition. With a lower cetane
number fuel a compression ignition (diesel) engine tends
to be more difficult to start and may run more noisily
when cold. There is a general preference, therefore, for
a diesel fuel composition to have a high cetane number,
and as such automotive diesel specifications generally
stipulate a minimum cetane number. Many diesel fuel
compositions contain cetane boost additives, also known
as ignition improvers, to ensure compliance with such
specifications.
It is known to include fatty acid alkyl esters
(FAAEs), in particular fatty acid methyl esters, in
diesel fuel compositions. An example of a FAAE included
in diesel fuels is rapeseed methyl ester (RME). FAAEs
are typically derivable from biological sources and may
be added for a variety of reasons, including to reduce
the environmental impact of the fuel production and
consumption process or to improve lubricity.
It is also well known that FAAEs often have higher
cetane numbers than typical diesel base fuels. For
example, the cetane number of soy methyl ester (SME) is
generally - 55, whereas that for a typical European
diesel base fuel is - 51-55.
Following conventional fuel formulation principles,
it would be expected that the cetane number of a base
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fuel/FAAE blend would vary linearly with FAAE
concentration. In other words, the addition of a FAAE to
a base fuel having a lower cetane number would be
expected to increase the cetane number of the fuel to an
extent directly proportional to the amount of FAAE added.
It has now been surprisingly discovered that FAAEs
can produce a non-linear change in cetane number when
blended with diesel base fuels. Based on this discovery,
the present invention is able to provide a more optimised
method for increasing the cetane number of a diesel fuel
composition to reach a particular target value.
According to a first aspect of the present invention
there is provided a method for increasing the cetane
number of a diesel fuel composition which contains a
major proportion of a diesel base fuel, in order to reach
a target cetane number X, which method comprises adding
to the base fuel an amount x of a fatty acid alkyl ester
(FAAE) having a cetane number B greater than the cetane
number A of the base fuel, wherein x is less than the
amount of the FAAE which would need to be added to the
base fuel in order to achieve cetane number X if linear
blending rules applied.
As described above, if linear blending rules applied
then the cetane number of the base fuel/FAAE mixture
would vary linearly with FAAE concentration. If this
were the case, it would then be straightforward to
calculate the amount of any given FAAE needed to increase
the cetane number of the base fuel to reach the target X.
However, it has now been found that, in particular at
lower concentrations, a FAAE can actually "boost" the
cetane number of a diesel base fuel above the level that
would be expected if linear blending rules applied. This
allows a lower amount of FAAE to be used to achieve any
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given target X, thus lowering any costs or other
detrimental effects associated with inclusion of the
FAAE.
Since it may be desirable to add a FAAE to a diesel
fuel composition for other reasons, for example to reduce
its environmental impact (including to reduce emissions)
and/or to improve its lubricity, the ability to use the
FAAE for the additional purpose of increasing the cetane
number can provide formulation advantages. Because the
FAAE can cause an unexpectedly high cetane number,
relatively small amounts may be used in some cases to
replace, either partially or wholly, other cetane
improvers which would otherwise be needed in the
composition, thus reducing the overall additive levels in
the composition and their associated costs.
In the present context, a "major proportion" of a
base fuel means typically 80% v/v or greater, more
suitably 90 or 95% v/v or greater, most preferably 98 or
99 or 99.5% v/v or greater. "Reaching" a target cetane
number can also embrace exceeding that number.
The FAAE will typically be added to the fuel
composition as a blend (i.e. a physical mixture),
conveniently before the composition is introduced into an
internal combustion engine or other system which is to be
run on the composition. Other fuel components and/or
fuel additives may also be incorporated into the
composition, either before or after addition of the FAAE
and either before or during use of the composition in a
combustion system.
The amount of FAAE added will depend on the natures
of the base fuel and FAAE in question and on the target
cetane number. In general, the volume fraction v of FAAE
in the resultant base fuel/FAAE mixture will be less than
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the volume fraction v' which would be required if linear
blending rules applied, wherein v' would be defined by
the equation :
X = A + v' (B-A) .
The volume fractions v and v' must each have a value
between 0 and 1. When carrying out the method of the
present invention the actual volume fraction of FAAE, v,
is preferably at least 0.02 lower than the "linear"
volume fraction v', more preferably at least 0.05 or 0.08
or 0.1 lower, most preferably at least 0.2, 0.3 or 0.5
lower and in cases up to 0.6 or 0.8 lower than v'. In
absolute terms, the actual volume fraction v is
preferably 0.25 or less, more preferably 0.2 or less, yet
more preferably 0.15 or 0.1 or 0.07 or less. It may for
example be from 0.01 to 0.25, preferably from 0.05 to
0.25, more preferably from 0.05 or 0.1 to 0.2.
Thus, as a result of carrying out the method of the
present invention, the concentration of the FAAE in the
overall fuel composition (or at least in the base
fuel/FAAE mixture) is preferably 25% v/v or less, more
preferably 20% v/v or less, yet more preferably 15 or 10
or 7% v/v or less. As a minimum it may be 0.05% v/v or
greater, preferably 1% v/v or greater, more preferably 2%
or 5% v/v or greater, most preferably 7 or 10% v/v or
greater.
Fatty acid alkyl esters, of which the most commonly
used in the present context are the methyl esters, are
already known as renewable diesel fuels (so-called
"biodiesel" fuels). They contain long chain carboxylic
acid molecules (generally from 10 to 22 carbon atoms
long), each having an alcohol molecule attached to one
end. Organically derived oils such as vegetable oils
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(including recycled vegetable oils) and animal fats can
be subjected to a transesterification process with an
alcohol (typically a C1 to C5 alcohol) to form the
corresponding fatty esters, typically mono-alkylated.
This process, which is suitably either acid- or base-
catalysed, such as with the base KOH, converts the
triglycerides contained in the oils into fatty acid
esters and free glycerol, by separating the fatty acid
components of the oils from their glycerol backbone.
In the present invention, the FAAE may be any
alkylated fatty acid or mixture of fatty acids. Its
fatty acid component(s) are preferably derived from a
biological source, more preferably a vegetable source.
They may be saturated or unsaturated; if the latter, they
may have one or more double bonds. They may be branched
or un-branched. Suitably they will have from 10 to 30,
more suitably from 10 to 22 or from 12 to 22, carbon
atoms in addition to the acid group(s) -CO2H. A FAAE
will typically comprise a mixture of different fatty acid
esters of different chain lengths, depending on its
source. For instance the commonly available rapeseed oil
contains mixtures of palmitic acid (C16), stearic acid
(C18), oleic, linoleic and linolenic acids (C18, with
one, two and three unsaturated carbon-carbon bonds
respectively) and sometimes also erucic acid (C22) - of
these the oleic and linoleic acids form the major
proportion. Soybean oil contains a mixture of palmitic,
stearic, oleic, linoleic and linolenic acids. Palm oil
usually contains a mixture of palmitic, stearic and
linoleic acid components.
The FAAE used in the present invention is preferably
derived from a natural fatty oil, for instance a
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vegetable oil such as rapeseed oil, soybean oil, coconut
oil, sunflower oil, palm oil, peanut oil, linseed oil,
camelina oil, safflower oil, babassu oil, tallow oil or
rice bran oil. It may in particular be an alkyl ester
(suitably the methyl ester) of rapeseed, soy, coconut or
palm oil.
The FAAE is preferably a Cl to C5 alkyl ester, more
preferably a methyl, ethyl or propyl (suitably iso-
propyl) ester, yet more preferably a methyl or ethyl
ester and in particular a methyl ester.
It may for example be selected from the group
consisting of rapeseed methyl ester (RME, also known as
rape oil methyl ester or rape methyl ester), soy methyl
ester (SME, also known as soybean methyl ester), palm oil
methyl ester (POME), coconut methyl ester (CME) (in
particular unrefined CME; the refined product is based on
the crude but with some of the higher and lower alkyl
chains (typically the C6, Cg, C10, C16 and C18) components
removed) and mixtures thereof. In general it may be
either natural or synthetic, refined or unrefined
("crude").
The FAAE suitably complies with specifications
applying to the rest of the fuel composition, and/or to
the base fuel to which it is added, bearing in mind the
intended use to which the composition is to be put (for
example, in which geographical area and at what time of
year). In particular, the FAAE preferably has a flash
point (IP 34) of greater than 101 C; a kinematic
viscosity at 40 C (IP 71) of 1.9 to 6.0 centistokes,
preferably 3.5 to 5.0 centistokes; a density from 845 to
910 kg/m3, preferably from 860 to 900 kg/m3, at 15 C (IP
365, EN ISO 12185 or EN ISO 3675); a water content (IP
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386) of less than 500 ppm; a T95 (the temperature at
which 95% of the fuel has evaporated, measured according
to IP 123) of less than 360 C; an acid number (IP 139) of
less than 0.8 mgKOH/g, preferably less than 0.5 mgKOH/g;
and an iodine number (IP 84) of less than 125, preferably
less than 120 or less than 115, grams of iodine (I2) per
lOOg of fuel. It also preferably contains (eg, by NMR)
less than 0.2% w/w of free methanol, less than 0.02% w/w
of free glycerol and greater than 96.5% w/w esters. In
general it may be preferred for the FAAE to conform to
the European specification EN 14214 for fatty acid methyl
esters for use as diesel fuels.
The measured cetane number of the FAAE (ASTM D613)
is suitably 55 or greater, preferably 58 or 60 or 65 or
even 70 or greater.
Two or more FAAEs may be added to the base fuel in
accordance with the present invention, either separately
or as a pre-prepared blend, so long as their combined
effect is to increase the cetane number of the resultant
composition to reach the target number X. In this case
the total amount x' of the two or more FAAEs must be less
than the amount of that same combination of FAAEs which
would need to be added to the base fuel in order to
achieve the target cetane number X if linear blending
rules applied for both or all of the FAAEs.
The FAAE preferably comprises (i.e. either is or
includes) RME or SME.
The FAAE may be added to the fuel composition for
one or more other purposes in addition to the desire to
increase cetane number, for instance to reduce life cycle
greenhouse gas emissions, to improve lubricity and/or to
reduce costs.
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The cetane number of a fuel composition may be
determined in known manner, for instance using the
standard test procedure ASTM D613 (ISO 5165, IP 41) which
provides a so-called "measured" cetane number obtained
under engine running conditions.
More preferably the cetane number may be determined
using the more recent and accurate "ignition quality test
(IQT)" (ASTM D6890, IP 498/03), which provides a
"derived" cetane number based on the time delay between
injection and combustion of a fuel sample introduced into
a constant volume combustion chamber. This relatively
rapid technique can be used on laboratory scale (ca.
100m1) samples of a range of different diesel fuels.
Alternatively, cetane number may be measured by near
infrared spectroscopy (NIR), as for example described in
US-A-5349188. This method may be preferred in a refinery
environment as it can be less cumbersome than for
instance ASTM D613. NIR measurements make use of a
correlation between the measured spectrum and the actual
cetane number of the sample. An underlying model is
prepared by correlating the known cetane numbers of a
variety of fuel samples (in this case, for example,
diesel base fuels, FAAEs and/or blends thereof) with
their near infrared spectral data.
The method of the present invention preferably
results in a diesel fuel composition which has a derived
cetane number (IP 498/03) of 50 or greater, more
preferably of 51 or 52 or 53 or greater.
The method of the present invention may additionally
or alternatively be used to adjust any property of the
diesel fuel composition which is equivalent to or
directly associated with cetane number.
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The diesel base fuel used in the composition may be
any known diesel base fuel, and it may itself comprise a
mixture of diesel fuel components. It will preferably
have a sulphur content of at most 2000 ppmw (parts per
million by weight). More preferably it will have a low
or ultra low sulphur content, for instance at most 500
ppmw, preferably no more than 350 ppmw, most preferably
no more than 100 or 50 or even 10 ppmw, of sulphur. The
resultant mixture of the base fuel and the FAME will also
preferably have a sulphur content within these ranges.
In some cases it may be preferred that the base fuel
is not a sulphur free ("zero sulphur") fuel.
Typical diesel fuel components comprise liquid
hydrocarbon middle distillate fuel oils, for instance
petroleum derived gas oils. Such base fuel components
may be organically or synthetically derived. They will
typically have boiling points within the usual diesel
range of 150 to 400 C, depending on grade and use. They
will typically have densities from 0.75 to 0.9 g/cm3,
preferably from 0.8 to 0.86 g/cm3, at 15 C (IP 365) and
measured cetane numbers (ASTM D613) of from 35 to 80,
more preferably from 40 to 75 or 70. Their initial
boiling points will suitably be in the range 150 to 230 C
and their final boiling points in the range 290 to 400 C.
Their kinematic viscosity at 40 C (ASTM D445) might
suitably be from 1.5 to 4.5 centistokes.
Such fuels are generally suitable for use in a
compression ignition (diesel) internal combustion engine,
of either the indirect or direct injection type.
Again, the fuel composition which results from
carrying out the present invention will also preferably
fall within these general specifications. In particular,
its measured cetane number will preferably be from 45 to
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70 or 80, more preferably from 50 to 65 or at least
greater than 50 or even 53 or 55 or 57.
A petroleum derived gas oil may be obtained from
refining and optionally (hydro)processing a crude
petroleum source. It may be a single gas oil stream
obtained from such a refinery process or a blend of
several gas oil fractions obtained in the refinery
process via different processing routes. Examples of
such gas oil fractions are straight run gas oil, vacuum
gas oil, gas oil as obtained in a thermal cracking
process, light and heavy cycle oils as obtained in a
fluid catalytic cracking unit and gas oil as obtained
from a hydrocracker unit. Optionally a petroleum derived
gas oil may comprise some petroleum derived kerosene
fraction.
Such gas oils may be processed in a
hydrodesulphurisation (HDS) unit so as to reduce their
sulphur content to a level suitable for inclusion in a
diesel fuel composition.
In the method of the present invention, the base
fuel may be or contain another so-called "biodiesel" fuel
component, such as an alcohol (in particular methanol or
ethanol) or other oxygenate or a vegetable oil or
vegetable oil derivative.
It may be or contain a Fischer-Tropsch derived fuel,
in particular a Fischer-Tropsch derived gas oil. Such
fuels are known and in use in diesel fuel compositions.
They are, or are prepared from, the synthesis products of
a Fischer-Tropsch condensation reaction, as for example
the commercially used gas oil obtained from the Shell
Middle Distillate Synthesis (Gas To Liquid) process
operating in Bintulu (Malaysia).
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The diesel fuel composition which results from the
method of the present invention may if desired contain
no, or only low levels of, other cetane improving
(ignition improving) additives such as 2-ethylhexyl
nitrate (EHN). In other words, the present invention
embraces the use of a FAAE in a diesel fuel composition
for the purpose of reducing the level of cetane improving
additives in the composition. As described above, the
amount of FAAE used to achieve a given reduction in
additive level will be less than the amount that would be
necessary if linear blending of the FAAE and base fuel
applied.
In this context, "use" of a FAAE in a fuel
composition means incorporating the FAAE into the
composition, typically as a blend (i.e. a physical
mixture) and optionally with one or more other fuel
components (such as diesel base fuels) and optionally
with one or more fuel additives. The FAAE is
conveniently incorporated before the composition is
introduced into an engine or other combustion system
which is to be run on the fuel composition. Instead or
in addition the use may involve running a diesel engine
on the fuel composition containing the FAAE, typically by
introducing the composition into a combustion chamber of
the engine.
The term "reducing" embraces reduction to zero; in
other words, the FAAE may be used to replace one or more
cetane improving additives either partially or
completely. The reduction may be as compared to the
level of the relevant additive(s) which would otherwise
have been incorporated into the fuel composition in order
to achieve a desired target cetane number, for instance
in order to meet government fuel specifications or
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consumer expectations. Thus the FAAE can help in
reducing the overall additive levels in the composition
and their associated costs.
Preferably the FAAE is used to reduce the w/w
concentration of the relevant additive(s) in the fuel
composition by at least 10%, more preferably by at least
20 or 30%, yet more preferably by at least 50 or 70 or 80
or even 90% or, as described above, by 100%.
It may for instance be used to replace cetane
improving additive(s) to an extent that the concentration
of cetane improving additives remaining in the fuel
composition is 300 ppmw or less, preferably 200 ppmw or
less, more preferably 100 or 50 ppmw or less. Most
preferably it may be used to replace cetane improving
additive(s) substantially entirely, the fuel composition
being nearly or essentially free of such additives and
containing for example 10 or 5 ppmw or less, preferably 1
ppmw or less, of cetane improving additives.
(All additive concentrations quoted in this
specification refer, unless otherwise stated, to active
matter concentrations by mass. The term "cetane
improving additive" refers to additives, other than the
FAAE, which can increase the cetane number of a fuel or
otherwise improve its ignition quality.)
Subject to the above, a diesel fuel composition
prepared according to the present invention may contain
other components in addition to the diesel base fuel and
the FAAE. Typically such components will be incorporated
in fuel additives. Examples include detergents such as
polyolefin substituted succinimides or succinamides of
polyamines, for instance polyisobutylene succinimides or
polyisobutylene amine succinamides, aliphatic amines,
Mannich bases or amines and polyolefin (e.g.
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polyisobutylene) maleic anhydrides. Succinimide
dispersant additives are described for example in
GB-A-960493, EP-A-0147240, EP-A-0482253, EP-A-0613938,
EP-A-0557516 and WO-A-98/42808. Particularly preferred
are polyolefin substituted succinimides such as
polyisobutylene succinimides.
The additives may contain other components in
addition to the detergent. Examples are lubricity
enhancers such as amide-based additives; dehazers, e.g.
alkoxylated phenol formaldehyde polymers; anti-foaming
agents (e.g. polyether-modified polysiloxanes); anti-rust
agents (e.g. a propane-1,2-diol semi-ester of
tetrapropenyl succinic acid, or polyhydric alcohol esters
of a succinic acid derivative, the succinic acid
derivative having on at least one of its alpha-carbon
atoms an unsubstituted or substituted aliphatic
hydrocarbon group containing from 20 to 500 carbon atoms,
e.g. the pentaerythritol diester of polyisobutylene-
substituted succinic acid); corrosion inhibitors;
reodorants; anti-wear additives; anti-oxidants (e.g.
phenolics such as 2,6-di-tert-butylphenol, or
phenylenediamines such as N,N'-di-sec-butyl-p-
phenylenediamine); metal deactivators; and combustion
improvers.
Where the fuel composition contains one or more
ignition improvers (cetane improvers), these may be
selected from for example 2-ethylhexyl nitrate (EHN),
cyclohexyl nitrate, di-tert-butyl peroxide and those
disclosed in US-4208190 at column 2, line 27 to column 3,
line 21.
The fuel composition will suitably contain only a
minor amount of such additives. Thus unless otherwise
stated, the (active matter) concentration of each such
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additional component in the overall fuel composition is
preferably up to 1% w/w, more preferably in the range
from 5 to 1000 ppmw, advantageously from 75 to 300 ppmw,
such as from 95 to 150 ppmw.
It is particularly preferred that a lubricity
enhancer be included in the fuel composition, especially
when it has a low (e.g. 500 ppmw or less) sulphur
content. The lubricity enhancer is conveniently present
at a concentration from 50 to 1000 ppmw, preferably from
100 to 1000 ppmw, based on the overall fuel composition.
Additives may be added at various stages during the
production of a fuel composition; those added at the
refinery for example might be selected from anti-static
agents, pipeline drag reducers, flow improvers (e.g.
ethylene/vinyl acetate copolymers or acrylate/maleic
anhydride copolymers) and wax anti-settling agents. When
carrying out the method of the present invention, the
diesel base fuel may already contain such refinery
additives. Other additives may be added downstream of
the refinery.
The method of the present invention may form part of
a process for, or be implemented using a system for,
controlling the blending of a fuel. composition, for
example in a refinery. Such a system will typically
include means for introducing a FAAE and a diesel base
fuel into a blending chamber, flow control means for
independently controlling the volumetric flow rates of
the FAAE and the base fuel into the chamber, means for
calculating the volume fraction of the FAAE needed to
achieve a desired target cetane nurnber input by a user
into the system and means for directing the result of
that calculation to the flow control means which is then
operable to achieve the desired ~iolume fraction in the
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product composition by altering the flow rates of its
constituents into the blending chamber.
In order to calculate the required volume fraction,
a process or system of this type will suitably make use
of known cetane numbers for the base fuel and FAAE
concerned, and conveniently also a model predicting the
cetane number of varying concentration blends of the two
according to linear blending rules. The process or
system may then, according to the present invention,
select and produce a FAAE volume fraction lower than that
predicted by the linear blending model to be necessary.
It may use a so-called quality estimator which will
provide, using a model, a real-time prediction of the
cetane number of each resulting blend from available raw
process measurements, such as for example the NIR
measured cetane numbers and the volumetric flow rates of
the constituents. More preferably such a quality
estimator is calibrated on-line by making use of, for
example, the method described in WO-A-02/06905.
The method of the present invention may thus
conveniently be used to automate, at least partially, the
formulation of a diesel fuel composition, preferably
providing real-time control over the relative proportions
of the FAAE and base fuel incorporated into the
composition, for instance by controlling the relative
flow rates of the constituents.
In accordance with the present invention, "use" of a
FAAE in the ways described above may also embrace
supplying a FAAE together with instructions for its use
in a diesel fuel composition to increase the cetane
number to a particular target and/or to improve the
ignition quality of the composition and/or to reduce the
level of cetane improving additives in the composition.
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The FAAE may be supplied as a component of a formulation
suitable and/or intended for use as a diesel fuel
additive, in which case the FAAE may be included in the
formulation for the purpose of influencing its effects on
the ignition quality of a diesel fuel composition.
A second aspect of the present invention provides a
diesel fuel composition prepared, or preparable, using a
method according to the first aspect. This composition
contains a major proportion of a diesel base fuel which
preferably has a low sulphur content (for example, less
than 400 or preferably 300 ppmw) and/or a measured cetane
number (ASTM D613) of from 48 to 52.
The present invention also provides a method of
operating a diesel engine, and/or a vehicle which is
driven by a diesel engine, which method involves
introducing into a combustion chamber of the engine a
diesel fuel composition according to the second aspect.
The fuel composition may be used in this way for the
purpose of improving ease of fuel ignition during use of
the engine.
Preferred features of the second and other aspects
of the present invention may be as described above in
connection with the first aspect.
Other features of the present invention will become
apparent from the following examples. Generally speaking
the present invention extends to any novel one, or any
novel combination, of the features disclosed in this
specification (including the accompanying claims).
Moreover, unless stated otherwise, any feature disclosed
herein may be replaced by an alternative feature serving
the same or a similar purpose.
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Examples
These Examples demonstrate the effects of fatty acid
alkyl esters, in particular fatty acid methyl esters, on
the cetane numbers of various typical diesel base fuels.
The fatty acid methyl esters (FAMEs) tested were
rapeseed methyl ester (RME) and soy methyl ester (SME).
The base fuels tested were a typical German
specification sulphur-free ("zero sulphur") diesel fuel
Fl, a US specification diesel fuel F2, a summer grade
European specification ultra low sulphur diesel fuel F3
(without additives) and a diesel fuel F4 which was the
same as F3 but contained a standard refinery treatment
additive (single dose treat rate; contained no cetane
improvers).
The specifications for the base fuels Fl to F3 are
shown in Table A.
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Table A
Base Base Base
Fuel property Test fuel fuel fuel
method Fl F2 F3
Density @ 15 C (kg/m3) IP 365 837.1 843.7 830.4
Measured cetane ASTM D613 50.4 50.3 53.9
number
Kinematic viscosity @ IP 71 2.851 3.058 2.506
40 C (centistokes)
Distillation ( C) IP 123
IBP 175.2 211.5 168
10% recovery 211.1 233.2 201
20% 227.5 245.1 220
30% 242.6 256 240
40% 257.3 266.3 256
50% 271.1 275.1 269
60% 284.8 284.1 280.5
70% 299.3 294.2 291.5
80% 316.1 305.8 303.5
90% 337.4 322.2 319.5
95% 355.2 337.5 335.5
FBP 365.9 349.3 349
Cold filter plugging IP 309 -29 -12 -18
point ( C)
Cloud point ( C) IP 219 -9 -11.8 -11
Flash point ( C) IP 34 63.5 92.5 63
Sulphur (ppmw) ASTM D2622 9 290 27
Iodine number IP 84 8 9 18.12
Acid number (total) IP 139 0.02 0.04 0.05
(mgKOH/g)
Various blends of the fatty acid methyl esters
(FAMEs) and the base fuels were prepared, to assess the
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effect of FAME concentration on the ignition quality of
the resultant fuels.
Derived cetane numbers were determined for most
samples, using the ignition quality test (IQT) method IP
498/03. For some samples, measured (engine) cetane
numbers were also obtained according to the CFR Cetane
Engine method, ASTM D613.
Example 1 - effect of RME on cetane number
The effect of RME on both the measured and the
derived cetane numbers of various diesel base fuels was
assessed as described above. The results are shown in
Tables 1 to 4 for the base fuels Fl to F4 respectively.
The derived cetane number for the neat RME was 58.1.
CA 02591826 2007-06-21
WO 2006/067234 PCT/EP2005/057159
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CA 02591826 2007-06-21
WO 2006/067234 PCT/EP2005/057159
21
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x ~n
M IZ3;
Ln u,
00 00
Ln = .
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Ln
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Ln ~
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w -I w M 61
Ln m
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Ln ~ Ln
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CA 02591826 2007-06-21
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- 22 -
These data show a non-linear change in cetane number
with RME concentration, for all the base fuels tested.
In particular, they show a marked "boost" in cetane
number at lower RME concentrations, such as 20% v/v or
below. Thus in this regime, for any given RME
concentration the cetane number of the base fuel/RME
blend is higher than linear blending rules would have
predicted. Correspondingly, in order to achieve any
given target cetane number, a lower amount of the RME is
needed than if linear blending rules applied.
The trend is highlighted by the higher accuracy IQT
data.
The presence of the refinery additive in base fuel
F4 appears to have no significant impact on the ability
of the RME to enhance cetane number.
For the zero sulphur fuel Fl, it appears that
slightly higher FAME concentrations (e.g. 10% v/v or
greater) are needed to achieve such a significant cetane
number boost.
Example 2 - effect of SME on cetane number
The effect of SME (soy methyl ester) on both the
measured and the derived cetane numbers of the four base
fuels was assessed as described above. The results are
shown in Tables 5 to 8.
The derived cetane number for the neat SME was 71.4.
CA 02591826 2007-06-21
WO 2006/067234 PCT/EP2005/057159
23
N
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LO
~ N
44 44
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Ln Ln Ln
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r-I r-I
4) 4)
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CA 02591826 2007-06-21
WO 2006/067234 PCT/EP2005/057159
24
Ln
cm x c~ c X rn
Ln Ln
rn ~
N l~ N x 61
Ln L,
0) N
CD = = O C)
~
N CO O N Q0 l0
Ln Q0
Ln rI
~ -1 x 0~
Ln u-)
('') V
CL i [=.i
OC)
{ O = = ~ O = Ol
~ r--I [~ (D r-I CO tn
~:l Ln Ln Ln
4 I 4--I
~ (D
U) N U) rI
x r -Q
Ln Ln
= r I -r-I
[,i] N 00 fl C'~
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Ln Lf) Lr)
I I
00 ~
N N k ~ N N x
Ln Ln
r-I -{
4 I N 6l LO 4--I N N ~
O ~ = = O ~ = =
N 0 M (N a) O N
fn ~ un un U) r-I U-) un
ro ~ co ~
-Q .Q
'~ "C=
O N 0
~
=r-I (D ~-I -r-I ~ ~4
+) f-I (D ~:l
r~ ra 5:~ u)
rtS (0 ~4 -P r0 rd
-P U 'O
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F-i -- N 0 0 ~ -- a) TI 0
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> ~~ ~~
2 0\0 x 0\0 W W .-/ x
c!)
CA 02591826 2007-06-21
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- 25 -
Again these data show a non-linear boost in cetane
number at lower SME concentrations, for all base fuels.
As for RME, there is no statistically significant
difference in this effect between the additivated (F4)
and unadditivated (F3) fuels.
It can therefore be seen that a target increase in
cetane number may be achieved, for the base fuels, by
incorporating a FAAE in an amount smaller than the amount
that would be needed if linear blending applied. For
example in the case of the SME/F2 blends (see Table 6), a
target cetane number of 51.7 can be achieved using only
2% v/v SME, whereas if linear blending applied, one would
expect 15.8% v/v of SME to be needed to achieve the same
cetane number. Similarly a target cetane number of 56.5
can be achieved using only 7% v/v SME, whereas linear
blending rules would predict that 36.3% v/v of SME would
be needed to achieve this effect. (These figures are
derived cetane numbers, measured by the IP 498/03
method.)
