Note: Descriptions are shown in the official language in which they were submitted.
CA 02377464 2002-03-20
LOW TEMPERATURE STABLE DIESEL OIL/ALCOIiOL MIXTURES
Background of the invention
This invention relates to low temperature stable diesel oil / ethanol mixtures
and, more
particularly, to biodegradable solubliser additives that promote the low
temperature stability.
The hope afforded to nuclear fusion and hydrogen fuel cell technology is
likely to be years,
or perhaps decades, from commercial viability. In the meantime, demand for oil
continues to
r rise, resulting in increasing pressure to find alternative energy resources:
In particular, the
world's finite reserves of oil represent a non-renewable source of energy: For
this reason, it
is imperative to find ways to reduce the consumption of traditional petroleum-
based oil, and
increase the use of alternative, renewable fuels.
The powering of diesel engines accounts for a significant proportion of oil
consumption
worldwide. A typical diesel oil is a petroleum gas oil (middle distillate),
with additives
present in very small amounts relative to the diesel oil. These additives
improve the
combustion efficiency of the diesel, oil, resulting in increased engine
efficiency and
performance, as well as reduced particulate emissions. For example, United
States Patent
4,451,266 teaches a corresponding additive that can be mixed with diesel oil
in a 1:500 to
1:2000 ratio, the additive comprising 3-10% methanol or ethanol, 3-13%
halogenated alkene,
3-13% aromatic hydrocarbon, 35-70% of naptha range hydrocarbon, and 20-30% of
hydroxy-
substituted unsaturated fatty acids.
To date, research in this field has investigated the production of alternative
fuel blends with
reduced diesel oil content, capable of powering a diesel engine. In some
cases, fuels have
been developed which lack diesel oil as a constituent. For example, United
States Patent
4,929,252 discloses an castor oil/ethanol,blend that may be used to power a
diesel engine. In
another example; United States Patent 4,937,655 discloses a vegetable
oil/ethanol mixture for
use as a diesel engine fuel, wherein the addition of a ketal, acetal or
orthoester to the mixture
converts any trace of contaminating water .to alcohol, thus discouraging phase
separation of
the oil/ethanol mix. Whilst these "bio-oil" fuels represent interesting
alternatives to
hydrocarbon-containing fuels, they inevitably contain a high proportion of
glycerides. In this
regard, it is well understood in the art that use of these fuels can often
give rise to glyceride
pyrolysis, which unavoidably results in engine gumming. The resulting buildup
of deposits
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within the engine can result in poor engine performance and efficiency. In
addition, the high
viscosity of "bio-oil" fuels can affect their compatibility for direct use in
a diesel engine. In
some cases, diesel engines must be significantly modified to accommodate the
specific
characteristics of these alternative fuels:
In the light of the problems encountered with "bio-oil" fuels, more recent
innovations in
diesel engine fuel technology have focussed upon fuel blends that include a
proportion of
diesel oil: In particular, it is well known in the art that ethanol can be
used in diesel oil
blends to produce a fuel suitable for use in a diesel engine: Ethanol confers
several
advantages over alternative constituents. Ethanol can be easily produced on an
industrial
scale, and thus represents a readily renewable source of energy. As an
oxygenate, it could
enhance combustion characteristics.
The key difficulty in providing a diesel oil / ethanol fuel blend, suitable
for use in a diesel
engine, arises from the limited miscibility of the two components. Although
small amounts
of ethanol and diesel oil are miscible at room temperature, slight
contamination with water
separates the mixture into two phases. In addition, the miscibility of diesel
oil and ethanol is
reduced at lower temperatures. One way of mixing diesel oil and ethanol
involves the
production of micro-emulsions. For example, United States Patent 4,477,258
discloses a
diesel fuel emulsion comprising diesel oil and an aqueous solution of ethanol
or methanol
together with an emulsifying blend of ~orbitan monooleate and a water soluble
ethoxylated
non-ionic surfactant. In another example, Unites Sates Patent 4,451,265
discloses a hybrid
diesel fuel composition in which water and alcohol are held in a stable
microemulsion by
means of a surfactant system comprising N,N-dimethylethanolamine and a long
chain fatty
acid.
It must be mentioned that, to maintain a thermodynamically stable emulsion,
the size of the
alcohol droplets must be very small. This in turn requires a large quantity of
surfactant in the
fuel blend. In this regard, surfactant is a relatively expensive constituent,
and the cost of the
resulting fuel can be unacceptably high. Microemulsions have a further
disadvantage with
regard to production costs: The production of stable microemulsions requires
intensive
mixing/stirring high volumes of fuel on an industrial scale that escalates the
production cost
even higher. Further, when a diesel fuel tank is filled with the emulsion
fuel, one must
remain with the particular emulsion fuel; and cannot be switched to regular
diesel fuel. This
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is because when emulsion fuel is diluted by regular diesel, the stability of
emulsion fuel
deteriorates resulting in phase separation.
As an alternative to microemulsions, it is also possible to mix diesel oil and
alcohol together
as a solution, which relies upon the miscibility of the two components. Diesel
oil and
anhydrous ethanol are readily miscible at room temperature: However, it is
well known in
the art that lower temperatures, or a small amount of contaminating water,
result in the
separation of the diesel oil and ethanol into distinct phases. A fuel that is
easily prone to
phase separation is unsuitable for use in a diesel engine: For this reason, it
is highly desirable
to produce diesel oil / ethanol fuel blends in which the diesel oil and
ethanol form a
homogeneous and stable solution.
In one attempt to achieve this objective, United States Patent 4,405,337
discloses a diesel oil /
alcohol fuel blend comprising a solubliser in the form of castor oil. In this
example, the
castor oil is shown to induce the miscibility of the diesel oil and an aqueous
solution of
alcohol, wherein the alcohol component comprises 0.5% water. At 25°C
the castor oil
induces solublisation of the diesel oil and alcohol at most relative
concentrations of the
constituents. However, at 10°C and at 0°C the solublisation
characteristics are limited. Fuel
mixtures comprising less than 20% castor oil, and more than 20% ethanol, will
generally
separate into two phases at 0°C. US 4,405,337 does not disclose the use
of castor oil fuel
blends at temperatures below 0°C.
In another example, United States Patent 6,017,369 discloses fuel compositions
comprising
diesel oil, ethanol, an alkyl ester of a fatty acid, and a stabilizer (of
specific ether or
ether/amide mixtures). Fuel blends comprising diesel oil / ethanol solutions
are described
that are stable at temperatures as low as -19°C. Such fuel blends
comprise a complex mixture
of additives to achieve reasonable levels of low temperature stability.
In the developed world, vehicles that are,powered by diesel engines comprise
the majority of
smaller vans and trucks, and nearly all large trucks, buses and non-
electrically powered
trains. In Europe, diesel oil powered cars comprise an increasingly
significant market share.
This has resulted from a new generation of direct-injection engines, which are
more refined
and powerful than their predecessors. 'The modern diesel engine is
considerably more
efficient than the equivalent gasoline engine, so further improvements to
generate "greener"
diesel engines, which use even less hydrocarbon-based fuel, could play a key
role in the
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reduction of petroleum consumption and the protection of the environment.
However, the
development of alternative "hybrid" diesel engine fuels has so far been
restricted by the
limitation of temperature stability. Much of the developed world exists in
regions of cold
climates with temperatures frequently falling below 0°C. Other regions
with less cold
climates nevertheless experience cold conditions during the winter months.
Therefore, to be
commercially viable, any new fuel for a diesel engine must have the property
of low
temperature stability:
It is an object of the present invention to provide improved low temperature
stable diesel
fuels, in the form of homogeneous liguid mixtures of diesel oil and alcohol,
comprising a
biodegradable oxygenate as a solubliser. Furthermore, it is an object the
present invention to
provide a solubliser that may be used in low concentrations to successfully
achieve
homogeneity of diesel oil / alcohol mixtures at low temperatures, without the
risk of
glyceride pyrolysis. It is'a further object of the present invention to
provide fuel blends that
exhibit superior levels of stability at temperatures of less than 0°C,
preferably less than -S°C.
Summary of Invention
The present invention provides low temperature stable diesel fuel compositions
which
comprise diesel oil, ethanol, and a solubliser comprising fatty acids having
chain lengths of
C,4_~g. The inclusion of specific fatty acids in diesel oil / ethanol fuel
blends can induce the
formation of stable homogeneous solutions at temperatures considerably lower
than 0°C, e:g.
as low as -20°C. In the fuel composition of the present invention, it
is important to note that
the components are dissolved in one anotherand the fuel is free of emulsions.
The ethanol
and diesel oil are typically present in the proportion of 5:95 to 85:15 by
weight. The
solubliser is typically added to the diesel oil / ethanol mixture in an amount
up to 20% by
weight based on the total fuel composition. The solubliser can be a fatty acid
derived from a
variety of biodegradable sources. Particularly useful solublisers include tall
oil and depitched
tall oil (tall oil from which heavy bottoms material has been removed).
Depitched tall oil is
free of glycerides and thus very suitable as a diesel fuel component.
Importantly, tall oil has
been unexpectedly found to provide for significantly improved temperature
stability of diesel
oil / ethanol solutions; thus permitting larger proportions of ethanol to
remain dissolved in
diesel oil at lower ambient temperatures. The fuels of the present invention
may be widely
used to power diesel engines under conditions where low ambient temperature is
an
important consideration.
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Description of the Drawings
Figure 1 is a graph to show the phase separation characteristics of diesel oil
/ ethanol
mixtures over a range of depitched tall oil concentrations;
Figure 2 is a graph to compare the volume of the separate (ethanol) phase of
azeotropic
ethanol / diesel oil mixtures in the presence or absence of depitched tall oil
(wherein D=diesel
oil, ZE=azeotropic ethanol, and DPTO=depitched tall oil);.
Figure 3 is a graph to compare the capacity of depitched tall oil, canola
methyl esters and
corn methyl esters, to solublise diesel oil and ethanol (wherein D=diesel oil;
ZE=azeotropic
ethanol, CAME=canola methyl esters; and COME=corn methyl esters); and
Figure 4 is a graph to analyze the capacity of canola methyl esters to
solublise diesel oil
ethanol mixtures aver a range of temperatures (wherein E=anhydrous ethanol;
D=diesel oil,
and CAME=canola methyl esters).
Detailed description of the preferred embodiments
Examples are provided with particular reference to depitched tall oil as a
solubliser. Tall oil
is a by-product of the pulping of resinous softwoods such as spruce and pine.
Pulp spent
liquor is treated with sulfuric acid before being collected as crude tall oil.
In this way, the
sufuric acid reacts with glycerides present in the liquor. Crude tall oil
comprises fatty acids
in the C~6 to C24 range, but the principle components are unsaturated CL8
fatty acids,
diterpenic rosin acids and unsaponifiable neutrals such as sterols. Crude tall
oil also contains
a small amount of sugars. However, when crude tall oil is depitched the rosin
acids, neutrals
and sugars remain in the heavy ends, an thus depitched tall oil comprises
primarily C~6 to Cps
fatty acids. The composition of depitched tall oil therefore provides
significant advantages
over diesel oil / ethanol solublisers of the prior art, since prior treatment
with sulfuric acid
renders the oil substantially free of gycerides, thus resulting in reduced
glyceride pyrolysis
during combustion.
Ex, ample 1
A series of tests were conducted on different mixtures of anhydrous ethanol,
#2 diesel oil,
and a solubliser as shown in Table 1 below:
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Table 1
Diesel oil ethanol mixtures with a solubliser Cetane Flash
number point
Certified #2 diesel oil only 45.7 86
Swt% ethanol + 94wt% #2 diesel + lwt% depitched 43.1 16
tall oil
Swt% ethanol + 94wt% #2 diesel + iwt% esterified 43.3
canola oil
Swt% ethanol + 94wt% #2 diesel + lwt% esterified 43.2
corn oil
Swt% ethanol + 94wt% #2 diesel+ lwt% esterified 43.6
soy oil
l Owt% ethanol + 88wt% #2 diesel + 2wt% depitched 39.5 15
tall oil
20wt% ethanol + 76wt% #2 diesel + 4wt% depitched 33.2 15
tall oil
The cetane numbers and flash points were determined as shown above. In
consideration of
Table l, the cetane numbers remain high for fuel mixtures comprising only S%
ethanol.
However, at higher ethanol concentrations the cetane numbers are lower.
Therefore, the
diesel fuel mixtures of the present invention, which comprise higher
concentrations of
ethanol, may require additional spiking to ensure suitable combustion
characteristics. From
Table 1, it will be noted that fuels comprising more than 5% ethanol have
lower flash points.
It is expected that combustion of such fuel mixtures will result in lower NOx
emissions as a
result of the lower combustion temperatures. Moreover, the ethanol, a simple
oxygenate, in
the mixtures will also result in reduced particulate emissions. Therefore, the
fuel mixtures
may present significant advantages in terms of reduced environmental
pollutants.
Example 2
The fuel mixtures containing depitched tall oil were tested for temperature
stability: This was
done by measuring the temperature at which phase separation takes place. As
the solubliser,
fatty acids in the form of depitched tall oil have been found to be
particularly effective. The
graph shown in Figure 1 displays the boundaries of phase separation for
anhydrous ethanol
and diesel oil at different temperatures and tall oil concentrations. Figure 1
demonstrates that
tall oil considerably enhances the capacity of ethanol and diesel oil to form
a solution.
Two general considerations can be made regarding Figure 1. Firstly, the graph
shows that
diesel oil f ethanol mixtures, comprising roughly equal quantities (by-
weight) of each
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component, require the highest amount of tall oil additive to ensure that a
homogeneous
solution is maintained. This point is xelevant regardless of the temperature.
In mixtures
comprising unequal amounts of diesel oil and ethanol, a smaller amount of tall
oil may be
added to achieve homogeneity. The second consideration relates to temperature.
Figure l
demonstrates that at lower temperatures; more tall oil is required to achieve
homogeneity of a
particular diesel oil /ethanol mixture.
In general, higher amounts of tall oil are needed to ensure complete
solublisation of diesel oil
and ethanol at lower temperatures. In the prior art; similar observations have
been made with
alternative solublisers. However, it is important to note that solublisers of
the prior art are
required in unsatisfactorily high concentrations to achieve solublisation at
low temperatures.
This is known in the art to potentially give rise to engine gumming and poor
engine
efficiency. In contrast, the present invention discloses a fuel that is stable
at low
temperatures, wherein the solubliser can generally be used in concentrations
that are
considerably lower than those of the prior art. Accordingly, the fuel
compositions of the
present invention are expected to be less prone to engine gumming and poor
engine
efficiency.
According to Figure 1, at -15°C the highest amount of tall oil needed
is ar~ly about 9% of the
total volume by weight. With mixtures comprising unequal amounts of diesel oil
and
ethanol, the amount of tall oil required is even lower. The unexpected
superior solublisation
properties of tall oil and other similar oils over the solublisers of the
prior art represent a
significant development in the formulation of "greener" diesel engine fuels,
which comprise
lower amounts of non-replaceable hydrocarbon-based oil products.
From Figure 1 it is also apparent that for a particular diesel oil / ethanol
mixture, the amount
of tall oil required :increases linearly as the temperature decreases. Based
on these results, it
is expected that diesel oil l ethanol mixtures can be obtained that are stable
at temperatures of
-40°C or lower with the addition of less than 20% tall oil. Depitched
tall oil is free of sugar
and glycerides. Therefore, the fuels of the present invention have the
potential to be used
successfully in diesel engines at ambient temperatures that are considerably
lower than 0°C.
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Example 3 Depitched tall oil descreases phase separation of diesel oil /
azeotropic ethanol
solutions
Water contamination of diesel oil / ethanol solutions can result in phase
separation of the
diesel oil and ethanol. It is known in the art that azeotropic ethanol
(ethanol containing 4%
water) does not readily form a solution with diesel oil. Experiments were
performed to
determine the ability of depitched tall oil to increase the solubility of
diesel oil 'and azeotropic
ethanol. Diesel oil / azeotropic ethanol' mixtures comprising 10%, 20% and 30%
azeotropic
ethanol were analyzed at temperatures ranging from -15°C to 20°C
(Figure 2). The graph
demonstrates that separation of the mixtures into 2 distinct phases occurred
at all azeotropic
ethanol concentrations, regardless of the presence of depitched tall oil.
However, for
azeotropic ethanol concentrations of 10% or 20%, the presence of depitched'
tall oil in the
mixtures significantly reduced the volume of the separated (ethanol) phase for
all
temperatures tested. The depitched tall oil therefore induced the ability of
the azeotropic
ethanol to homogeneously dissolve in the diesel oil.
Example 4 Comparison of depitched tall oil with methyl esters of canola and
corn
Further experimentation was carried out using a diesel fuel mixture comprising
5%
azeotropic ethanol (Figure 3), to compare the solublisation capacities of
depitched tall oil
with canola methyl esters and corn methyl esters. In the absence of additive,
the mixture
remained in two phases at all temperatures tested (-15°C to
20°C; Figure 3). However, when
a small amount of depitched tall oil was added to the mixture, the homogeneity
was achieved
at temperatures ranging from 10°C to 20°C, although a very small
second phase appeared at
temperatures lower~than S°C (Figure 3). These results suggest that the
fuel mixtures of the
present invention should preferably comprise less than 0.2% moisture.
The solublisation characteristics of depitehed tall oil were compared with
those of canola
methyl esters and corn methyl esters. Unexpectedly, the canola and corn methyl
esters
decreased the ability of the mixture to form a homogeneous solution at all
temperatures
tested, resulting in an increase in the volume of the separated (ethanol)
phase. This was in
complete contrast to: the depitched tall oil, which increased the homogeneity
o~ the mixture
significantly. In conclusion, when moisture is present, the depitched tall oil
exhibits
properties that induce the formation of diesel oil / ethanol solutions, unlike
the selected
methyl esters tested.
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Example 5 Depitched tall oil is a si nig_ ficantly more efficient solubliser
than canola methyl
esters for diesel oil /'anhydrous ethanol mixtures
Experiments were carried out to analyze the ability of canola methyl esters to
solubli a
mixtures of diesel oil and anhydrous ethanol (Figure 4). The presence of
canola methyl esters
can maintain homogeneity of mixtures comprising 10% ethanol (anhydrous), only
at
temperatures higher than 0°C. (0.5% and 2% methyl ester concentration
produces near
identical results). Therefore, the performance of depitched tall oil as a
solubliser is far
superior to that of canola methyl esters. In this regard, a 2% concentration
of depitched tall
oil can maintain a fuel mixture comprising 10% anhydrous ethanol at
temperatures as low as
-15°C (see Figure l).
When the anhydrous ethanol concentration is increased to 30%, canola methyl
esters (up to
6%) will only maintain a homogeneous solution above 10°C. However, the
superior
solublisation properties of depitched tall oil (at 7%) maintain the same fuel
mixture as a
homogeneous solution at temperatures as low as -15°C (see Figure 1).
In conclusion; depitched tall oil exhibits diesel oil / anhydrous ethanol
solublisation
properties that are signi#icantly superior to those of canola methyl esters.
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