U.S. patent application number 13/721499 was filed with the patent office on 2013-06-27 for organic nitrates as ignition enhancers.
This patent application is currently assigned to SHELL OIL COMPANY. The applicant listed for this patent is SHELL OIL COMPANY. Invention is credited to Widyai Prenish BANSIE, Matthias Eggenstein, Andrew David Horton, Renate Uitz.
Application Number | 20130160354 13/721499 |
Document ID | / |
Family ID | 47436016 |
Filed Date | 2013-06-27 |
United States Patent
Application |
20130160354 |
Kind Code |
A1 |
BANSIE; Widyai Prenish ; et
al. |
June 27, 2013 |
ORGANIC NITRATES AS IGNITION ENHANCERS
Abstract
A diesel fuel composition comprising an organic nitrate is
described. The organic nitrate may be a terpene nitrate. Methods of
using an organic nitrate for achieving a desired cetane number, and
uses of organic nitrates for the purpose of reducing the ignition
delay of the fuel and/or for increasing its cetane number to a
defined level are also described, as are methods of operating a
compression ignition engine.
Inventors: |
BANSIE; Widyai Prenish;
(Amsterdam, NL) ; Eggenstein; Matthias; (Hamburg,
DE) ; Uitz; Renate; (Hamburg, DE) ; Horton;
Andrew David; (Amsterdam, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SHELL OIL COMPANY; |
Houston |
TX |
US |
|
|
Assignee: |
SHELL OIL COMPANY
Houston
TX
|
Family ID: |
47436016 |
Appl. No.: |
13/721499 |
Filed: |
December 20, 2012 |
Current U.S.
Class: |
44/324 |
Current CPC
Class: |
C10L 2300/20 20130101;
C10L 10/12 20130101; C10L 2270/026 20130101; C10L 1/231 20130101;
C10L 1/231 20130101; C10L 2300/20 20130101 |
Class at
Publication: |
44/324 |
International
Class: |
C10L 10/12 20060101
C10L010/12 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2011 |
EP |
11195433.5 |
Claims
1. A diesel fuel composition for use in a compression ignition
engine, said diesel fuel composition comprises an organic nitrate
selected from the group consisting of: a cyclic nitrate of Formula
(4): ##STR00023## and Formula (4A): ##STR00024## wherein each of
R.sub.1 to R.sub.9 is independently selected from H or
C.sub.1-C.sub.6 alkyl, or nitrate(--ONO.sub.2), wherein optionally
one of R.sub.4 and R.sub.5 forms an optionally substituted alkylene
bridge with one of R.sub.8 and R.sub.9, which may be substituted by
one or more C.sub.1-C.sub.6 alkyl, and/or nitrate(--ONO.sub.2);
wherein at least one of R.sub.1 to R.sub.9 is not H, and provided
that no more than one R.sub.2 to R.sub.9 comprises a nitrate
group.
2. The diesel fuel composition of claim 1, wherein at least one of
R.sub.1 to R.sub.9 is selected from methyl, ethyl, n-propyl,
isopropyl, n-butyl, isobutyl, and tert-butyl.
3. The diesel fuel composition of claim 1, wherein one of R.sub.4
and R.sub.5 is methyl and one of R.sub.8 and R.sub.9 is
isopropyl.
4. The diesel fuel composition of claim 1, wherein one of R.sub.4
and R.sub.5 forms an optionally substituted alkylene bridge with
one of R.sub.8 and R.sub.9; and wherein the alkylene bridge has the
formula --(CR.sub.aR.sub.b).sub.n--, wherein R.sub.a and R.sub.b
are independently selected from H, methyl, ethyl, n-propyl,
isopropyl, n-butyl, isobutyl and tert-butyl; and n is 1 or 2.
5. The diesel fuel composition of claim 4, wherein the cetane
number improver is defined by Formula (5): ##STR00025## or Formula
(5A): ##STR00026## wherein (i) at least two of R.sub.a, R.sub.b,
R.sub.2, R.sub.3 and R.sub.9 are methyl; (ii) R.sub.a and R.sub.b
are methyl; (iii) R.sub.2 and R.sub.3 are methyl; (iv) R.sub.a,
R.sub.b and R.sub.9 are methyl; or (iv) R.sub.2, R.sub.3 and
R.sub.9 are methyl.
6. The diesel fuel composition of claim 1, wherein the cetane
number of the diesel fuel composition containing the organic
nitrate is higher than the cetane number of the diesel fuel
composition lacking the organic nitrate.
7. The diesel fuel composition of claim 1, wherein said diesel fuel
composition has a cetane number of between 52 and 58.
8. The diesel fuel composition of claim 1, wherein the diesel fuel
composition comprises one or more additional organic nitrate.
9. A method for reducing the ignition delay and/or increasing the
cetane number of a diesel fuel composition, said method comprises
adding to the composition an amount of an organic nitrate, wherein
the organic nitrate is selected from the group consisting of: a
cyclic nitrate of Formula (4): ##STR00027## and Formula (4A):
##STR00028## wherein each of R.sub.1 to R.sub.9 is independently
selected from H or C.sub.1-C.sub.6 alkyl, or nitrate(--ONO.sub.2),
wherein optionally one of R.sub.4 and R.sub.5 forms an optionally
substituted alkylene bridge with one of R.sub.8 and R.sub.9, which
may be substituted by one or more C.sub.1-C.sub.6 alkyl, and/or
nitrate(--ONO.sub.2); wherein at least one of R.sub.1 to R.sub.9 is
not H, and provided that no more than one R.sub.2 to R.sub.9
comprises a nitrate group.
10. The method of claim 9, wherein at least one of R.sub.1 to
R.sub.9 is selected from methyl, ethyl, n-propyl, isopropyl,
n-butyl, isobutyl, and tert-butyl.
11. The method of claim 9, wherein one of R.sub.4 and R.sub.5 is
methyl and one of R.sub.8 and R.sub.9 is isopropyl.
12. The method of claim 9, wherein the cetane number improver is
defined by Formula (5): ##STR00029## or Formula (5A): ##STR00030##
wherein (i) at least two of R.sub.a, R.sub.b, R.sub.2, R.sub.3 and
R.sub.9 are methyl; (ii) R.sub.a and R.sub.b are methyl; (iii)
R.sub.2 and R.sub.3 are methyl; (iv) R.sub.a, R.sub.b and R.sub.9
are methyl; (iii) R.sub.2, R.sub.3 and R.sub.9 are methyl.
13. The method of claim 9, wherein said method is configured to
increase the cetane number of the diesel fuel composition to
achieve a target cetane number.
14. The method of claim 9 further comprising adding one or more
additional organic nitrate to the fuel composition.
15. The method of claim 9, wherein said method is configured to
reduce the amount of 2-ethylhexyl nitrate (2-EHN) in the diesel
fuel composition to achieve the target cetane number.
16. The diesel fuel composition of claim 1, wherein the organic
nitrate is present in the diesel fuel composition at a
concentration of: (a) between 0.025% and 2.0% w/w; (b) between
0.05% and 1.0% w/w; or (c) 0.05% w/w, 0.1% w/w, 0.5% w/w or 1.0%
w/w; based on the total weight of the fuel composition.
17. The diesel fuel composition of claim 1, wherein the organic
nitrate is further defined as follows: (i) R.sub.1, R.sub.6 and
R.sub.7 are H; (ii) R.sub.1, R.sub.6 and R.sub.7 are H; R.sub.2 and
R.sub.3 are methyl; (iii) R.sub.1, R.sub.6 and R.sub.7 are H;
R.sub.5 is H and R.sub.9 is methyl; or (iv) R.sub.1, R.sub.6 and
R.sub.7 are H; R.sub.2 and R.sub.3 are methyl; R.sub.5 is H and
R.sub.9 is methyl.
18. The diesel fuel composition of claim 1, wherein the organic
nitrate is selected from the group consisting of: bornyl nitrate,
fenchyl nitrate, and menthly nitrate.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority of European
Patent Application No. 11195433.5, filed on Dec. 22, 2011, the
disclosure of which is incorporated by reference herein in its
entirety.
FIELD OF THE INVENTION
[0002] Embodiments of the present invention relate to a method of
improving diesel fuels, and in particular to the use of organic
nitrates as additives in a diesel fuel composition to give
improvements in fuel combustion and cetane number.
BACKGROUND OF THE INVENTION
[0003] This section is intended to introduce various aspects of the
art, which may be associated with exemplary embodiments of the
present invention. This discussion is believed to assist in
providing a framework to facilitate a better understanding of
particular aspects of the present invention. Accordingly, it should
be understood that this section should be read in this light, and
not necessarily as admissions of any prior art.
[0004] The cetane number of a fuel composition is a measure of its
ease of ignition and combustion. 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; conversely a fuel of
higher cetane number tends to impart easier cold starting, to lower
engine noise, to alleviate white smoke ("cold smoke") caused by
incomplete combustion after.
[0005] There is a general preference, therefore, for a diesel fuel
composition to have a high cetane number, a preference which has
become stronger as emissions legislation grows increasingly
stringent, and as such automotive diesel specifications generally
stipulate a minimum cetane number. To this end, many diesel fuel
compositions contain ignition improvers, also known as cetane boost
additives or cetane (number) improvers/enhancers, to ensure
compliance with such specifications and generally to improve the
combustion characteristics of the fuel.
[0006] Organic nitrates have been known for some time as ignition
accelerants in fuels, and some are also known to increase the
cetane number of diesel fuels. Such organic nitrates generally
include short- and medium-chain linear and branched alkanols and
nitrates of cycloalkanols, such as those described in U.S. Pat. No.
4,479,905.
[0007] A commonly used diesel fuel ignition improver is
2-ethylhexyl nitrate (2-EHN), which operates by shortening the
ignition delay of a fuel to which it is added. However, 2-EHN is
also a radical initiator, and can potentially have an adverse
effect on the thermal stability of a fuel. Poor thermal stability
in turn results in an increase in the products of instability
reactions, such as gums, lacquers and other insoluble species.
These products can block engine filters and foul fuel injectors and
valves, and consequently can result in loss of engine efficiency or
emissions control.
[0008] The organic nitrates described in the prior art as
combustion improvers and/or cetane number improvers have a series
of disadvantages, especially lack of thermal stability, excessively
high volatility and insufficient efficacy. However, it may be
expected that by decreasing the volatility of a cetane enhancer,
e.g. by using a molecule of higher molecular weight, its efficacy
as a combustion improver and/or cetane number improver may then
decline.
[0009] There are also health and safety concerns regarding the use
of 2-EHN, which is a strong oxidising agent and is also readily
combustible in its pure form. It can also be difficult to store in
concentrated form as it tends to decompose, and so is prone to
forming potentially explosive mixtures. Furthermore, it has been
noted that 2-EHN functions most effectively under mild engine
conditions.
[0010] These disadvantages, taken together with the often
significant cost of incorporating 2-EHN as an additive into a fuel
composition, mean that it would be generally desirable to reduce or
eliminate the need for 2-EHN and other known cetane number
improvers in diesel fuel compositions, whilst at the same time
maintaining acceptable combustion properties.
[0011] WO2008/000778 describes one such approach to reducing the
amount of an ignition enhance required in a diesel fuel by using a
Fischer-Tropsch derived fuel component, in a fuel composition
containing an ignition improver, which acts to enhance the effect
of the ignition improver and thus reduce the amount required to
achieve the same desired cetane number.
[0012] WO2006/067234 relates to the use of fatty acid alkyl esters
(FAAEs) in diesel fuels to increase the cetane number.
[0013] Thus, it is desirable to overcome or alleviate at least one
of the problems associated with the prior art.
SUMMARY OF THE INVENTION
[0014] Embodiments of the invention provide alternative organic
nitrates which are effective as combustion improvers or cetane
number improvers. Embodiments of the invention also provide
alternative organic nitrates which have similar or lower volatility
than known cetane number improvers, or which meet acceptable safety
levels for use in commercial diesel fuels. In addition, embodiments
of the invention provide alternative organic nitrates for use as
ignition/combustion improvers and that are most cost-effective
and/or more convenient to manufacture than known organic nitrate
cetane number improvers. Also, embodiments of the invention provide
alternative organic nitrates for use as cetane number enhancers
that work well under harsh engine conditions (for example, some
known cetane enhancers may undesirably over-advance combustion.
Embodiments of the invention further provide cetane enhancers
derived from renewable (or waste) feedstocks or by-products.
Additionally, embodiments of the invention provide methods for
producing organic nitrates useful as cetane number improvers by
nitration of corresponding organic alcohols.
[0015] Surprisingly, it has been found that certain long chain
linear organic nitrates, certain cyclic terpene organic nitrates,
and certain nitrates derived from fatty alcohols and fatty acid
alkyl esters can serve to reduce the ignition delay and/or as
effective cetane number improvers in diesel fuels.
[0016] Accordingly, in a first aspect of the invention, there is
provided a diesel fuel composition for use in a compression
ignition engine, which comprises an organic nitrate selected from
the group consisting of:
[0017] a cyclic nitrate of Formula (4):
##STR00001##
wherein each of R.sub.1 to R.sub.9 is independently selected from H
or C.sub.1-C.sub.6 alkyl, or nitrate(--ONO.sub.2), wherein
optionally one of R.sub.4 and R.sub.5 forms an optionally
substituted alkylene bridge with one of R.sub.8 and R.sub.9, which
may be substituted by one or more C.sub.1-C.sub.6 alkyl, and/or
nitrate(--ONO.sub.2); wherein at least one of R.sub.1 to R.sub.9 is
not H, and provided that no more than one R.sub.2 to R.sub.9
comprises a nitrate group.
[0018] In one embodiment, the organic nitrate has the effect of
increasing the cetane number of fuel, such as to a desired or
target cetane number.
[0019] One or more additional organic nitrates may be used in the
diesel fuel composition. Embodiments of the present invention also
define the addition organic nitrates.
[0020] In one embodiment, the diesel fuel composition has a cetane
number of 40 or more, 50 or more, 60 or more, or 70 or more.
[0021] In another aspect of the invention, there is provided a
method for reducing the ignition delay and/or increasing the cetane
number of a diesel fuel composition, which method comprises adding
to the composition an amount of an organic nitrate according to the
invention.
[0022] The method may involve increasing the cetane number of the
diesel fuel composition to achieve a target cetane number. In some
embodiments, the method may involve adding one or more additional
organic nitrate to the fuel composition.
[0023] In one embodiment, the method may further be for reducing
the amount of 2-ethylhexyl nitrate (2-EHN) or any other known
cetane enhancer in the diesel fuel composition to achieve the
target cetane number.
[0024] A further aspect of the invention is directed to the use of
an organic nitrate in a diesel fuel composition for the purpose of
reducing the ignition delay (ID) of the diesel fuel composition,
wherein the organic nitrate is as defined herein.
[0025] The diesel fuel composition of this or any other aspect may
comprise a biofuel, and optionally may comprise FAAEs, such as
FAMEs.
[0026] The organic nitrate may be present in the diesel fuel
composition at a concentration of: (a) between 0.025% and 2.0% w/w;
(b) between 0.05% and 1.0% w/w; or (c) one of 0.05% w/w, 0.1% w/w,
0.5% w/w or 1.0% w/w; based on the total weight of the fuel
composition.
[0027] In a preferred embodiment, the organic nitrate is selected
from the group consisting of bornyl nitrate, fenchyl nitrate,
menthly nitrate, and any combination thereof.
[0028] The embodiments of the present invention may additionally or
alternatively be used to adjust any property of the fuel
composition which is equivalent to or associated with cetane
number, for example, to improve the combustion performance of the
fuel composition, e.g. to shorten ignition delays (i.e. the time
being fuel injection and ignition in a combustion chamber during
use of the fuel), to facilitate cold starting or to reduce
incomplete combustion and/or associated emissions in a
fuel-consuming system running on the fuel composition) and/or to
improve fuel economy or exhaust emissions generally.
[0029] Accordingly, in further aspects of the invention there is
provided a method or use of an organic nitrate in a diesel fuel
composition for improving the fuel economy of an engine into which
the fuel composition is or is intended to be introduced, or of a
vehicle powered by such an engine, wherein the organic nitrate is
defined herein.
[0030] In yet another aspect of the invention there is provided a
method for the preparation of a diesel fuel composition having a
target cetane number for use in a compression ignition engine. The
method comprises adding an organic nitrate, as defined elsewhere
herein, to the diesel fuel composition; and blending the organic
nitrate with the diesel fuel composition to provide a diesel fuel
composition having the target cetane number.
[0031] Still yet another aspect of the invention relates to a
method of operating a compression ignition engine and/or a vehicle
which is powered by such an engine, which method involves
introducing into a combustion chamber of the engine a diesel fuel
composition as defined elsewhere herein, or as obtained by the uses
and methods of the invention.
[0032] Other features of embodiments of the present invention will
become apparent from the following detailed description. It should
be understood, however, that the detailed description and the
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
invention will become apparent to those skilled in the art from
this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The invention is further illustrated by the accompanying
drawings in which:
[0034] FIG. 1 depicts the structures of exemplary embodiments of
organic nitrates according to aspects of the invention;
[0035] FIG. 2 illustrates the reduction in ignition delay (ID) as a
percentage for a diesel base fuel comprising certain embodiments of
the organic nitrates according to aspects of the invention;
[0036] FIG. 3 illustrates the results of derived ignition quality
(DIQ) studies for a diesel base fuel comprising an exemplary
embodiment of organic nitrates according to aspects of the
invention under certain combustion conditions;
[0037] FIG. 4 is a graph illustrating correlations between the
measured ignition delay at the various combustion conditions (a01
to a11--see Key) against the organic nitrate used as a cetane
enhancer in a diesel fuel composition according to the invention.
The results are shown against molecular weight of the cetane
enhancer: bornyl nitrate (1), menthyl nitrate (2), 1,10-decyl
dinitrate (3), oleyl nitrate (4), hexadecyl nitrate (5),
nitro-substituted methyl oleate (6), and nitro-substituted ethyl
abietate (7); and
[0038] FIG. 5 is a differential scanning calorimetry
(DSC)/thermogravimetric analysis (TGA) plot illustrating the
thermal decomposition of 1,10-decyl dinitrate.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0039] In order to assist with the understanding of the invention
several terms are defined herein.
[0040] The terms "cetane (number) improver" and "cetane (number)
enhancer" are used interchangeably to encompass any component that,
when added to a fuel composition at a suitable concentration, has
the effect of increasing the cetane number of the fuel composition
relative to its previous cetane number under one or more engine
conditions within the operating conditions of the respective fuel
or engine. The term cetane number improvers/enhancers of the
invention are organic nitrates as described herein. As used herein,
a cetane number improver or enhancer may also be referred to as a
cetane number increasing additive/agent or the like.
[0041] In one embodiment, the cetane number of a fuel composition
may be determined in any 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. In a preferred embodiment, the cetane number may be
determined using the more recent and accurate "ignition quality
test" (IQT; ASTM D6890, IP 498), 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
100 ml) samples of a range of different fuels. Alternatively,
cetane number may be measured by near infrared spectroscopy (NIR),
as for example described in U.S. Pat. No. 5,349,188. 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 a sample. An underlying model is prepared by
correlating the known cetane numbers of a variety of fuel samples
with their near infrared spectral data.
[0042] In some embodiments, the methods/uses encompass adding a
cetane enhancer according to aspects of the present invention to a
fuel composition so as to adjust the cetane number or to achieve or
reach a desired target cetane number. In the context of the
embodiments of this invention, to "reach" a target cetane number
can also embrace exceeding that number. Thus, the target cetane
number may be a target minimum cetane number.
[0043] In one embodiment, the present invention results in a fuel
composition which has a derived cetane number (IP 498) of 50 or
greater, more preferably of 51, 52, 53, 54 or 55 or greater. For
example, in some embodiments, the resultant fuel composition may
have a cetane number of 60 or greater, 65 or greater or even 70 or
greater.
[0044] Embodiments of the present invention may additionally or
alternatively be used to adjust any property of the fuel
composition which is equivalent to or associated with cetane
number, for example, to improve the combustion performance of the
fuel composition, e.g. to shorten ignition delays (i.e. the time
between fuel injection and ignition in a combustion chamber during
use of the fuel), to facilitate cold starting or to reduce
incomplete combustion and/or associated emissions in a
fuel-consuming system running on the fuel composition) and/or to
improve fuel economy or exhaust emissions generally.
[0045] In accordance with embodiments of the invention, therefore,
cetane number improvers also encompass additives that increase the
combustability of the fuel to which it is added and, as such,
decrease the ignition delay. Therefore, as used herein, an organic
nitrate that increases the combustability (i.e. a "combustion
enhancer/improver") and/or decreases the ignition delay (i.e. an
"ignition enhancer/improver") is also considered to be a cetane
number improver or enhancer.
[0046] Cetane number improvers of the invention may be used to
increase the cetane number of a fuel composition. As used herein,
an "increase" in the context of cetane number embraces any degree
of increase compared to a previously measured cetane number under
the same or equivalent conditions. Thus, in a preferred embodiment,
the increase is compared to the cetane number of the same fuel
composition prior to incorporation of the cetane number increasing
(or improving) component or additive. Alternatively, the cetane
number increase may be measured in comparison to an otherwise
analogous fuel composition (or batch or the same fuel composition)
that does not include the cetane number enhancer of the invention.
Alternatively, an increase in cetane number of a fuel relative to a
comparative fuel may be inferred by a measured increase in
combustability or a measured decrease in ignition delay for the
comparative fuels.
[0047] The increase in cetane number (or the decrease in ignition
delay, for example) may be measured and/or reported in any suitable
manner, such as in terms of a percentage increase or decrease. By
way of example, the percentage increase or decrease may be at least
1%, such as at least 2%. In one embodiment, the percentage increase
in cetane number or decrease in ignition delay is at least 5%, at
least 10%, at least 15% or at least 20%. In some embodiments, the
increase in cetane number or decrease in ignition delay may be at
least 25%, at least 30%. However, it should be appreciated that any
measurable improvement in cetane number or ignition delay may
provide a worthwhile advantage, depending on what other factors are
considered important, e.g. availability, cost, safety and so
on.
[0048] The engine in which the fuel composition of the invention is
used may be any appropriate engine. Thus, where the fuel is a
diesel or biodiesel fuel composition, the engine is a diesel or
compression ignition engine Likewise, any type of diesel engine may
be used, such as a turbo charged diesel engine, provided the same
or equivalent engine is used to measure fuel economy with and
without the cetane number increasing component. Similarly, the
invention is applicable to an engine in any vehicle. Generally, the
cetane number improvers of the invention are suitable for use over
a wide range of engine working conditions. However, some organic
nitrates of the invention may provide optimal effects under a
particular narrow range of engine working conditions, such as under
mild conditions and more suitably under harsh conditions.
[0049] Cetane Number Enhancers/Ignition Improvers
[0050] Cetane number enhancers are known and commercially
available, and may also be known (in the context of diesel fuels)
as "cetane (number) improvers", "combustion improvers" and
"ignition improvers" etc. as previously described.
[0051] Cetane enhancers are often added to diesel fuels, at
additive levels (typically 0.1 to 2.0% w/w), to improve the
combustion properties of the fuel. They function to reduce the
ignition delay, i.e. the period between the time of injection of
the fuel and the start of combustion (ignition). This, in turn,
leads to better engine performance, for example, in terms of higher
fuel efficiency, lower emissions, reduced combustion noise and
improved cold starting. Addition of a cetane enhancer to a diesel
fuel allows the point in the diesel cycle at which heat is released
to be advanced, which results in improved thermodynamic efficiency
(maximum efficiency at about 10.degree. after top dead centre.
[0052] Although there are various explanations of the working of
cetane enhancers, such as their effect in increasing the heating
rate of the fuel, it is generally accepted that they act as sources
of chain-initiating radicals.
[0053] The cetane number (CN) of a fuel is defined by reference to
the ignition properties of standard mixtures of n-hexadecane
(cetane, CN=100) and 2,2,4,4,6,8,8-hepta-methylnonane (CN=15). A
fuel with a high CN has a short ignition delay. Typically,
molecules with high octane numbers, which confer a resistance to
spontaneous ignition in gasoline spark ignition engines, have low
cetane numbers. The addition of small amounts of cetane enhancers
to a diesel fuel may, therefore, result in improved fuel properties
based on the shorter ignition delay.
[0054] Known cetane number enhancers include: a) certain organic
nitrates (e.g. isopropyl nitrate, 2-ethylhexyl nitrate (2-EHN),
cyclohexyl nitrate, and methoxyethyl nitrate); b) organic peroxides
and hydroperoxides (e.g. di-tert-butyl peroxide); and c) organic
peracids and peresters. The most commonly used cetane enhances are
dialkylperoxides (ROOR, di-t-butylperoxide) and organic nitrates
(R--ONO.sub.2), of which the most important is 2-ethylhexylnitrate
(2-EHN). European consumption of 2-EHN grew from 75 kt/a to 101
kt/a from 2000 to 2008, and an average annual growth of
approximately 3.5% has been predicted from 2008 to 2013.
[0055] The consumption of 2-EHN in North America (USA: 7.2 kt/a in
2008) is much lower than in Europe.
[0056] 2-EHN is produced industrially by the nitration of
2-ethylhexanol, and in Europe this consumes almost a quarter of the
production of this alcohol. The nitration of the alcohol involves
reaction with a 1/1 mixture of undiluted nitric and sulfuric acids
(using stoichiometric amounts of alcohol and nitric acid).
[0057] There are some safety concerns surrounding the production,
transport and use of 2-EHN. For example, it is conceivable that
2-EHN drums exposed to high temperatures during transport could be
subject to runaway decomposition reaction. The low flash point of
2-EHN (76.degree. C.) is also a concern. Furthermore, the
auto-ignition temperature of 2-EHN of 130.degree. C. is lower than
normal hydrocarbons. There have been very many studies of the
thermal stability of 2-EHN (e.g. Pritchard (1989), Combustion and
Flame, 75, 415; Bornemann & Scheidt (2000), F. Int. J. Chem.
Kinetics, 34, 34; and Zeng et al. (2008), J. Thermal Analysis &
calorimetry, 91, 359).
[0058] Accordingly, it was desired to identify further alternative
cetane number improvers, which may provide benefits over the known
cetane enhancer. Any useful benefit may be achieved, such as in
relation to their synthesis, storage, transportation; or in use,
e.g. under certain operating conditions or in certain diesel fuels.
Particular benefits of the invention are directed to one or more of
the following: increased stability under storage and transport
conditions; at least equal and more suitably greater effectiveness
as a cetane enhancer; organic nitrates derivable from renewable
feedstocks or waste streams; effectiveness under harsh engine
conditions; and effectiveness at component or more suitably at
additive concentration levels.
[0059] Thus, embodiments of the present invention provide
alternative organic nitrates for use as cetane number improvers in
diesel fuels and optionally for achieving one or more associated
benefit.
[0060] The cetane number improver according to aspects of the
invention may be selected from nitrated:
[0061] (a) terpene alcohols, particularly monoterpene alcohols and
most preferably monocyclic and bicyclic molecules including
pinenes, such as borneol, fenchol and menthol;
[0062] (b) fatty alcohols, particularly obtained by hydrogenation
of fatty acid esters (e.g. the synthetic alcohol mixture, Neodol
23, derived from the SHF process)
[0063] (c) unsaturated fatty esters, particularly FAMEs, such as
methyl oleate;
[0064] (d) tall oil derived resin esters, particularly abietate
esters such as ethyl abietate; and
[0065] (e) long-chain linear alkanols, particularly linear
C.sub.10-C.sub.18 alkanols and diols, such as 1-octanol,
1,10,-decanediol, 1-dodecenol, 1-tridecanol, 1-tetradecanol,
1-hexadecanol, 1-octadecanol; and any combination thereof.
[0066] Accordingly, the cetane number improver has one or two
nitrate (NO.sub.3) groups in place of the hydroxyl groups in the
above-mentioned compounds.
[0067] With the exception of 1,10,-decanediol, generally the
alcohol feedstocks are commercially available at scales of at least
10 kt/a, which would potentially be compatible with production of
new useful cetane enhancers for worldwide consumption.
1,10-decanediol may be obtained by the hydrogenation of sebacic
acid (1,8-octanedicarboxylic acid), which itself is produced via
the alkali fusion of ricinoleic acid, the major constituent of
castor oil.
[0068] Thus, in accordance with a first embodiment of the
invention, the cetane number improver of the invention has the
Formula (1): R--ONO.sub.2, wherein R is a terpene or an oxygenated
(saturated) terpene. Optionally, the terpene may be natural or
substituted by up to three (e.g. 1, 2 or 3) C.sub.1-C.sub.6 alkyl
groups or a further nitrate (--ONO.sub.2) group.
[0069] Terpenes are classified according to the number of units of
the basic structure methylbuta-1,3-diene or isoprene, which make up
the terpene. Monoterpenes contain two isoprene units and are
generally considered to have the chemical formula C.sub.10H.sub.16.
However, monoterpenes are particularly sensitive to oxygenation at
the carbon-carbon double bond and so monoterpenes are typically
saturated hydrocarbons lacking the carbon-carbon double bond. These
oxygenated, saturated molecules are sometimes also referred to as
monoterpenes, and are encompassed by the term "monoterpene" as used
in the context of this invention. Monoterpenoid is another term
that is understood to include the monoterpenes and other related
compounds having the monoterpene skeleton, and such monoterpenoid
structures are also encompassed within the definition of
monoterpene used herein.
[0070] Monoterpenes may be acyclic such as myrcene and ocimene or
cyclic such as limonene and pinene. In one embodiment, the terpene
is a monocyclic or a bridged-monocyclic (i.e. bicyclic) alkyl.
[0071] In one embodiment, the cetane enhancer of the invention has
the Formula (2): C.sub.10H.sub.16X--ONO.sub.2, wherein X is
selected from H, C.sub.1-C.sub.6 alkyl and ONO.sub.2. In a
preferred embodiment, X is selected from H, methyl, ethyl and ONO2;
and still more preferably, X is H. Most preferably, R of Formula
(1) is a monoterpene selected from menthyl, fenchyl and bornyl,
which may optionally be substituted by X as defined above.
[0072] According to embodiments of the invention, therefore, the
cetane number improver may be a compound of Formula (3):
##STR00002##
wherein each of R.sub.1 to R.sub.9 is independently selected from H
or C.sub.1-C.sub.6 alkyl, or nitrate(--ONO.sub.2), wherein
optionally two of R.sub.1 to R.sub.9 may be connected together to
form a bridge, which may be substituted by one or more
C.sub.1-C.sub.6 alkyl, and/or nitrate(--ONO.sub.2); provided that
no more than 1 R.sub.1 to R.sub.9 comprises a nitrate group. In one
embodiment, R.sub.1 to R.sub.9 are independently selected from H or
C.sub.1-C.sub.6 alkyl, wherein optionally one of R.sub.4 and
R.sub.5 forms an optionally substituted alkylene bridge with one of
R.sub.8 and R.sub.9. Preferably at least one of R.sub.1 to R.sub.9
is not H; more preferably 1, 2, 3, 4 or 5 of R.sub.1 to R.sub.9 is
not H.
[0073] The C.sub.1-C.sub.6 alkyl may be straight chain (i.e.
linear) or branched chain, wherein the number 1 to 6 refers to the
total number of carbon atoms in the group. In one embodiment,
C.sub.1-C.sub.6 alkyl radicals include methyl, ethyl, n-propyl,
isopropyl, n-butyl, isobutyl, tert-butyl, sec-butyl, n-pentyl,
isopentyl, tert-pentyl, sec-pentyl, n-hexyl, 2-ethylbutyl, and
2,3-dimethylbutyl.
[0074] In accordance with a preferred embodiment, R.sub.1 to
R.sub.9 are independently selected from H, methyl, ethyl, n-propyl,
isopropyl, n-butyl, isobutyl and tert-butyl, wherein optionally one
of R.sub.4 and R.sub.5 forms an optionally substituted alkylene
bridge with one of R.sub.8 and R.sub.9. In one embodiment, the
alkylene bridge has the formula --(CR.sub.aR.sub.b).sub.n--,
wherein R.sub.a and R.sub.b are independently selected from H,
methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and
tert-butyl; and n is 1 or 2. In a preferred embodiment, R.sub.a and
R.sub.b are independently selected from H, methyl and ethyl, and n
is 1; and yet more preferably selected from H and methyl, and n is
1.
[0075] In a preferred embodiment, R.sub.1, R.sub.6 and R.sub.7 are
H. In another preferred embodiment R.sub.1, R.sub.6 and R.sub.7 are
H, one of R.sub.4 and R.sub.5 is H, one of R.sub.8 and R.sub.9 is
H, and the other of R.sub.4 and R.sub.5, and R.sub.8 and R.sub.9 is
selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl
and tert-butyl or they are connected together to form an alkylene
bridge of the formula --CR.sub.aR.sub.b--, wherein R.sub.a and
R.sub.b are defined above. In one particularly preferred
embodiment, one of R.sub.4 and R.sub.5 is H, and the other is
methyl; and one of R.sub.8 and R.sub.9 is H, and the other is
isopropyl; wherein R.sub.1, R.sub.2, R.sub.3, R.sub.6 and R.sub.7
are as defined in any of the above embodiments; preferably wherein
R.sub.1, R.sub.6 and R.sub.7 are H, and R.sub.2 and R.sub.3 are as
defined in any of the above embodiments; and most preferably
wherein R.sub.1, R.sub.2, R.sub.3, R.sub.6 and R.sub.7 are H.
[0076] In yet another particularly preferred embodiment of Formula
(3) or (3A), one of R.sub.4 and R.sub.5 is H, one of R.sub.8 and
R.sub.9 is H or methyl, and the other of R.sub.4 and R.sub.5 and of
R.sub.8 and R.sub.9 are connected together to form an alkylene
bridge of the formula --CR.sub.aR.sub.b--, wherein R.sub.a and
R.sub.b are H or methyl. Beneficially in this preferred embodiment,
one of R.sub.8 and R.sub.9 is methyl, R.sub.1, R.sub.6 and R.sub.7
are H, R.sub.a and R.sub.b are H or methyl, and R.sub.2 and R.sub.3
are as defined in any of the above embodiments. In one preferred
group of compounds of this embodiment, at least two of R.sub.a,
R.sub.b, R.sub.2 and R.sub.3 are methyl. For example, in one
embodiment R.sub.a and R.sub.b are methyl, and in another
embodiment R.sub.2 and R.sub.3 are methyl.
[0077] Accordingly, in another preferred embodiment of the
invention, the cetane number improver is defined by Formula
(4):
##STR00003##
wherein each of R.sub.1 to R.sub.9 is as defined in connection with
Formula (3). In one embodiment, at least one of R.sub.1 to R.sub.9
is not H, and more preferably, 1, 2, 3, 4 or 5 of R.sub.1 to
R.sub.9 is not H. In a preferred structure of Formula (4) or
Formula (4A), R.sub.8 and R.sub.4 are connected together to form an
alkylene bridge of the formula --(CR.sub.aR.sub.b).sub.n--, wherein
R.sub.a and R.sub.b are independently selected from H, methyl,
ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl; and n
is 1 or 2. More preferably the alkylene bridge has the formula
--CR.sub.aR.sub.b--, wherein R.sub.a and R.sub.b are H or methyl.
Also preferred are compounds of Formula (4) and Formula (4A) in
which R.sub.1, R.sub.6 and R.sub.7 are H. Still more preferred are
compounds of Formula (4) and Formula (4A) wherein R.sub.1, R.sub.6
and R.sub.7 are H and at least two of R.sub.a, R.sub.b, R.sub.2 and
R.sub.3 are methyl. In one particular embodiment R.sub.a and
R.sub.b are methyl, and in another particular embodiment R.sub.2
and R.sub.3 are methyl.
[0078] In yet another preferred embodiment, the cetane number
improver is defined by Formula (5):
##STR00004##
or Formula (5A):
##STR00005##
[0079] wherein each of R.sub.1 to R.sub.3, R.sub.5 to R.sub.7,
R.sub.9, R.sub.a and R.sub.b are as defined in connection with any
embodiment of Formulas (3) or (3A), or as defined in connection
with any embodiment of Formulas (4) or (4A). Preferably, in the
compound of Formulas (5) and (5A), R.sub.1, R.sub.6 and R.sub.7 are
H; and R.sub.2, R.sub.3, R.sub.5, R.sub.9, R.sub.a and R.sub.b are
independently selected from H, methyl and ethyl. Beneficially at
least one of R.sub.2, R.sub.3, R.sub.5, R.sub.9, R.sub.a and
R.sub.b is not H, and preferably 1, 2 or 3 of R.sub.2, R.sub.3,
R.sub.5, R.sub.9, R.sub.a and R.sub.b is not H. Most preferred are
compounds wherein three of R.sub.2, R.sub.3, R.sub.5, R.sub.9,
R.sub.a and R.sub.b are methyl.
[0080] In the cetane number improver compounds of embodiments of
the invention, the nitrate may be arranged in an axial or
equatorial position relative to the alkyl ring. In a preferred
embodiment, however, the nitrate is attached in an equatorial
position on the ring.
[0081] Most preferred cetane improvers of this embodiment are
bornyl nitrate, fenchyl nitrate and menthly nitrate.
[0082] In accordance with another embodiment of the invention, the
cetane number improver is a compound of the Formula (6):
R.sub.x--ONO.sub.2, wherein R.sub.x is a linear (straight-chain)
aliphatic group having 8 to 24 carbon atoms. In one embodiment, the
aliphatic group has between 10 and 20 carbon atoms, and preferably
between 10 and 18 carbon atoms. For example, in one embodiment,
R.sub.x groups have 8, 10, 12, 13, 14, 16 or 18 carbon atoms. In a
preferred embodiment, R.sub.x group has 18 carbon atoms. The
aliphatic group may be saturated or unsaturated. When unsaturated
it is preferably mono-unsaturated. The R.sub.x group may optionally
be substituted with a nitrate (--ONO.sub.2) group to form a
dinitrate compound. Preferably the one to two nitrate groups are
attached to the terminal carbon atoms of the aliphatic group.
[0083] Embodiments of cetane enhancers of the invention of Formula
(6) include 1-octyl nitrate, 1,10,-decyl dinitrate, 1-dodecyl
nitrate, 1-tridecyl nitrate, 1-tetradecyl nitrate, 1-hexadecyl
nitrate, and 1-octadecyl nitrate.
[0084] In accordance with one embodiment, the R.sub.x group a fatty
acid derivative, particularly a fatty alcohol derivative. A
preferred fatty alcohol derivative is monounsaturated, and is more
preferably a cis-monounsaturated fatty alcohol derivative (i.e.
wherein adjacent hydrogen atoms are on the same side of the double
bond). Thus, in some embodiments, the cetane number improver of the
present invention has the Formula (7):
CH.sub.3(CH.sub.2).sub.xCH.dbd.CH(CH.sub.2).sub.yONO.sub.2
wherein X is between 3 and 8 and Y is between 4 and 9. In one
embodiment, X is between 5 and 7 and Y is between 6 and 8. In a
preferred embodiment, X is 5 or 7 and Y is 6 or 8. In another
preferred embodiment, the carbon-carbon double bond is in the cis
formation.
[0085] A preferred monounsaturated aliphatic nitrate of the
invention is oleyl nitrate.
[0086] In accordance with a third embodiment of the invention, the
cetane number improver of the invention is a nitro-substituted
fatty acid ester of the Formula (7):
R.sub.y-[O.sub.sNO.sub.t].sub.u, wherein R.sub.y is a alkyl ester
of a fatty acid, i.e. a fatty acid alkyl ester (FAAE) moiety, S is
0 or 1, t is 1 or 2, and u is 1 to 4 or 1 to 3.
[0087] In one embodiment, the FAAE group is a linear
(straight-chain) aliphatic group having 8 to 24 carbon atoms,
preferably between 10 and 22 carbon atoms, preferably between 12
and 20 carbon atoms, and most preferably between 14 and 18 carbon
atoms. For example, particularly suitable R.sub.y groups have 14,
16 or 18 carbon atoms; and advantageously the R.sub.y group has 18
carbon atoms. The aliphatic group may be saturated or unsaturated.
Preferably R.sub.y is mono-unsaturated, and more preferably the
R.sub.y group has a cis double-bond. The R.sub.y group may
optionally be substituted with one or two additional
nitro-substituted groups of formula O.sub.sNO.sub.t.
[0088] A preferred nitro-substituted fatty acid ester of the
invention is a methyl oleate substituted with 1, 2 or 3
O.sub.sNO.sub.t groups.
[0089] In accordance with yet another embodiment of the invention,
the cetane number improver of the invention is a nitro-substituted
diterpene of the Formula (8): R.sub.z--[O.sub.sNO.sub.t].sub.u,
wherein R.sub.1 is a diterpene or an alkyl ester of a diterpene,
and wherein [O.sub.sNO.sub.t].sub.u is as defined above. In one
embodiment, the compound of Formula (8) is an alkyl ester of
abietic acid. In a preferred embodiment, the ester is a methyl or
ethyl ester. The R.sub.z group may optionally be substituted with
one or two additional nitro-substituted groups of formula
O.sub.sNO.sub.t. In another preferred embodiment, the
nitro-substituted diterpene is nitro-substituted ethyl abietate
substituted with 1, 2 or 3 O.sub.sNO.sub.t groups.
[0090] In accordance with another embodiment of the invention, the
cetane number improver is a nitro-substituted steroid containing
from 1 to 3 nitrate groups, such as cholesterol nitrate.
[0091] In one embodiment, in use, the cetane number improving
additive of the invention may be pre-dissolved in a suitable
solvent, for example an oil such as a mineral oil or
Fischer-Tropsch derived hydrocarbon mixture; a fuel component
(which again may be either mineral or Fischer-Tropsch derived)
compatible with the diesel fuel composition in which the additive
is to be used (for example a middle distillate fuel component such
as a gas oil or kerosene); a poly alpha olefin; a so-called biofuel
such as a fatty acid alkyl ester (FAAB), a Fischer-Tropsch derived
biomass-to-liquid synthesis product, a hydrogenated vegetable oil,
a waste or algae oil or an alcohol such as ethanol; an aromatic
solvent; any other hydrocarbon or organic solvent; or a mixture
thereof. Preferred solvents for use in this context are mineral oil
based diesel fuel components and solvents, and Fischer-Tropsch
derived components such as the "XtL" components referred to below.
Biofuel solvents may also be preferred in certain cases. In one
embodiment, the cetane enhancer will be part of an additive
(performance) package additionally containing other additives such
as detergents, anti-foaming agents, corrosion inhibitors, dehazers
etc. Alternatively, the cetane enhancing agent of the invention may
be blended directly with the base fuel.
[0092] The concentration of the cetane number enhancing additive
used may depend on desirable fuel characteristics/properties, such
as: the desired combustability of the overall fuel composition; the
combustability of the composition prior to incorporation of the
additive; the combustability and/or stability of the additive
itself; and/or the properties of any solvent in which the additive
is used. By way of example, the concentration of the cetane number
improving additive in the fuel composition may be up to 2% w/w and
preferably up to 1.0% w/w. Thus, the concentration of the cetane
number improver may be from 0.025% w/w to 2% w/w, or from 0.05% w/w
to 1% w/w. In some cases, the concentration of the cetane number
improver is from 0.05% w/w to 1.0 w/w, such as 0.05% w/w, 0.1% w/w,
0.25% w/w, 0.5% w/w, 0.75% w/w or 1.0% w/w based on the total
weight of the fuel composition.
[0093] Where a combination of two or more cetane number improving
additives is used in the fuel composition, the same concentration
ranges may apply to the total combination of cetane number
improving additives. It will be appreciated that
amounts/concentrations may also be expressed as ppm, in which case
1% w/w corresponds to 10,000 ppm w/w.
[0094] The remainder of the composition will typically consist of
one or more automotive base fuels optionally together with one or
more fuel additives, for instance as described in more detail
below.
[0095] The relative proportions of the cetane number enhancer, fuel
components and any other components or additives present in a
diesel fuel composition prepared according to the invention may
also depend on other desired properties such as density, emissions
performance and viscosity.
[0096] The synthesis of embodiments of the cetane enhancers of the
invention are described further below.
Synthesis of Cetane Number Enhancers
[0097] A range of alcohols and olefins were evaluated as precursors
of cetane enhancers. The conversion of alcohols to nitrates is
generally well-known in the art (Olah et al. Nitration: Methods and
mechanisms, Chapter 4, Aliphatic nitration in Organic nitro
chemistry series, VCH, New York, 1989, p. 219; Boschan et al.
(1955) Chem. Rev., 55, 485), and any appropriate procedure can be
used to produce the organic nitrates of the invention.
[0098] Although olefinic substrates may afford nitrates (i.e.
R--ONO.sub.2) on reaction with typical nitrating agents (HNO.sub.3,
N.sub.2O.sub.4, N.sub.2O.sub.5 etc.), more typically they react to
give products with nitro (R--NO.sub.2) and other substituents.
Since nitroalkanes are inherently unstable (decomposing via both
non-radical, HONO elimination; and radical mechanisms, C--NO.sub.2
bond homolysis); like nitrates, they are potential sources of
radicals and may, therefore, also be useful as cetane
enhancers.
[0099] It was anticipated that, in most cases, the alcohols could
be easily converted to the corresponding nitrates by reaction with
nitric acid. Alcohol nitration involves attack of the --OH
functionality on NO.sub.2.sup.+, and may be generated using the
following reagents: (i) nitric acid for secondary alcohols; (ii) a
mixture of nitric acid, sulfuric acid and urea for primary or
secondary alcohols; and (iii) a mixture of nitric acid and acetic
anhydride (precursor of reactive acetyl nitrate) in acetic acid for
unsaturated alcohols.
[0100] The choice of reagent used to synthesise the nitrate or
nitro-compounds of the invention may depend on the reactivity of
the alcohol starting material and the desirability to avoid side
reactions, such as oxidation of the alcohol to a ketone, or
sulfation of the olefin. Reactive olefins, such as pinenes, can be
cleanly converted to nitrates, for example, by (ring-opening)
reaction with nitric acid (e.g. Canoira et al. (2007) Fuel, 86,
965; Bakhvalov et al. (2000) J. Organic Chem., 36, 1601; Bakhvalov
et al. (2002) J. Organic Chem., 38, 507). However, olefins
containing ester functionalities (such as unsaturated constituents
of FAME) may undergo partial hydrolysis of the ester under these
conditions, affording free acid, which is not desirable in a diesel
fuel component. In these cases, N.sub.2O.sub.4 may suitably be used
instead of nitric acid. Reaction with olefins normally, therefore,
results in a mixture of products, containing nitro (R--NO.sub.2),
as well as nitrate (R--ONO.sub.2) and hydroxyl functionalities.
[0101] Synthesis of embodiments of the cetane enhancing agents of
the invention were initially performed at small scale (ca. 2 g) to
investigate optimum conditions (e.g. yield, purity), and for safety
reasons. The reactions were then scaled up to afford 20 to 40 g of
the cetane enhancers, which (following thermal stability tests)
were sent for assays in a combustion research unit (CRU).
[0102] Following the synthesis of the organic nitrates, a
differential scanning calorimetry/thermal gravimetric analysis
(DSC/TGA measurement) was performed to determine the thermal
decomposition behaviour of the molecules, before shipping for
further analysis.
Conversion of Primary Alcohols
[0103] A common method of converting primary/secondary alcohols to
nitrates involves the use of mixed nitric and sulfuric acids (molar
ratio substrate: nitric acid: sulfuric acid generally 1:3:8),
together with urea (0.25 equivalent based on substrate). The urea
is used to remove any HNO.sub.2 (nitrous acid) formed. The mixed
acid is a more powerful nitrating agent than nitric acid alone, due
to the higher concentration of NO.sub.2.sup.+, which is the
reactive species. A general method is shown in Scheme 1 below.
##STR00006##
[0104] The primary alcohols were nitrated at 0.degree. C. for 2
hours. Following neutralisation, extraction with dichloromethane
and drying, the primary nitrates were obtained in a yield of
80-98%. Where a di-nitrate is to be synthesised from a di-hydroxy
starting material the relative proportions of reaction components
are selected to achieve two equivalents of HNO.sub.3 to ensure
complete conversion of hydroxyl groups. In some cases, lower than
expected yields of nitrated alkyls were obtained, which may be due
to dissolution of part of the nitrated product in the water
layer.
[0105] Exemplary nitrated alkyls (compounds 1 to 6) of the
invention are illustrated in FIG. 1.
Conversion of Secondary Alcohols
[0106] In some cases secondary alcohols may be nitrated using the
same reagent mixture and conditions as used for primary alcohols.
Alternatively, nitric acid may be used, which is a less powerful
oxidising agent than the mixed acid.
[0107] One exemplary secondary alcohol is endo-borneol, which may
be converted into a bornyl nitrate.
[0108] By way of example, the secondary alcohols may be nitrated by
reacting with nitric acid at room temperature (RT) for
approximately 24 hours. In another example, exo-borneol was reacted
with nitric acid at RT to obtain the exo-nitrate of borneol (see
reaction Scheme 2 below and FIG. 1, compound 7; yield 87%).
##STR00007##
[0109] Nitrated products from exo-fenchol and endo-fenchol may be
obtained in a similar manner to the borneol compounds (see reaction
Scheme 3 below). Unlike endo-fenchol, exo-fenchol is not
commercially available, but may be prepared by the reduction of
L-fenchone via a Meerwein-Ponndorf-Verley reduction (MPV; see e.g.
Huckel & Rohrer (1960) Chem. Ber., 93, 1053; Mojtahedi et al.
(2007) Org. Lett., 9, 2791). This was found to give a mixture of
the endo- and exo-fenchol in the ratio 1:3. The MPV reaction is an
aluminium-catalyzed hydride shift (of RCHOH), from the alcohol
(isopropanol) to the carbonyl carbon (L-fenchone). Isopropanol may
be used as a hydride donor, because the acetone formed can be
easily removed by distillation. The reaction was refluxed at
95.degree. C. for 7 days followed by an extraction. This mixture of
secondary alcohols was allowed to react with nitric acid for 24
hours at RT, to give a mixture of two nitrated compounds (see FIG.
1, compounds 8a, 8b) as the main products, together with unreacted
endo-fenchol. The sterically crowded endo-isomer appears not to
react with the milder nitrating reagent, whereas the exo-fenchol
affords the two isomeric nitrates, as confirmed by .sup.1H and
.sup.13C NMR spectroscopy.
##STR00008##
[0110] The secondary alcohol, menthol (e.g. L-isomer), may be
nitrated using the same conditions as for primary alcohols in
general (i.e. mixed acid; see Scheme 4). After extraction with
diethyl ether, the nitrated product (see FIG. 1, compound 9) was
obtained in a yield of 95%.
##STR00009##
Conversion of .alpha.-Terpineol
[0111] .beta.-pinene may be reacted with nitric acid, e.g. at
-15.degree. C. in dichloromethane, according to methods known to
the person of skill in the art (see reaction Scheme 5 below). After
neutralisation, the product may be isolated by extraction with
dichloromethane. NMR may be used to confirm the identity of the
product.
##STR00010##
[0112] As illustrated, this reaction proceeds via protonation of
the double bond in .beta.-pinene, followed by rearrangement
(.beta.-fragmentation) to relieve ring strain and attack of
NO.sub.3.sup.- on the tertiary carbonium ion.
[0113] Tertiary nitrates are generally known to be less thermally
stable than primary and secondary nitrates. Therefore, it may be
necessary to store and ship tertiary nitrates, such as
.alpha.-terpineol nitrate, with particular care.
Conversion of Unsaturated Alcohols
[0114] In general, unsaturated alcohols can be nitrated selectively
at the alcohol position to leave the double bond intact, provided
that the mode of introducing the reactants and the amount of
nitrating agent is suitably controlled, and the use of sulfuric
acid is avoided (as this may react with the double bond to give a
sulfate). Thus, any suitable method can be used.
[0115] By way of example, oleyl alcohol (e.g. cis-9-octadecen-1-ol)
was nitrated slowly adding nitric acid to a mixture of the alcohol
and acetic anhydride in acetic acid solvent at 15.degree. C. (see
Scheme 6 below). Advantageously, this embodiment avoids build-up of
significant concentrations of acetyl nitrate (which may undergo
runaway decomposition above 60.degree. C.). Acetyl nitrate is a
powerful nitrating agent, being a good source of NO.sub.2.sup.+,
which reacts with the alcohol. The product (FIG. 1, compound 10)
can then be extracted with a suitable solvent, such as diethyl
ether. 1H-NMR confirmed the clean formation of the desired single
product without significant by-products.
[0116] Nitration of unsaturated secondary alcohols, such as
cholesterol, may be performed similarly so as to form cholesterol
nitrate (compound 11) shown in FIG. 1.
##STR00011##
Conversion of Olefinic Esters
[0117] The formation of nitrate or nitro derivatives of olefins may
be carried out using any appropriate reaction scheme. Typically,
conditions used will be different to those described above for
non-olefinic esters. For example, it is desirable to avoid sulfuric
acid (to reduce risk of olefin sulfation). Exemplary conditions
include: (i) HNO.sub.3 (70%) and acetic anhydride (precursor of
acetyl nitrate); (ii) fuming HNO.sub.3, acetic acid and NaNO.sub.2;
(iii) N.sub.2O.sub.4 in chloroform or hexane.
[0118] When used in the nitration of FAMEs, processes (i) and (ii)
have been reported to result in the partial hydrolysis of the
ester. For example, scheme (i) has been found to form nitro/nitrate
and nitro/acetate products as well as nitro-substitution of the
allylic position. Scheme (ii) has been found to result in low
conversion rates of unsaturated FAMEs, with nitro-olefins formed in
low yields. Therefore, reaction scheme (iii) may be preferred,
since it is expected to avoid ester hydrolysis. N.sub.2O.sub.4 may
conveniently be used as a dilute solution (boiling point
30-100.degree. C.), and excess reagent removed under low pressure
at the end of the procedure. Chloroform and hexane were both used
as solvents.
[0119] Three unsaturated FAMEs and a resin ester were nitrated
using this procedure. In a typical reaction, methyl oleate was
added to a stock solution of N.sub.2O.sub.4 in chloroform at 0 C
and stirred for 48 hours. After, excess N.sub.2O.sub.4 was removed
in vacuo and the product quenched in an ice bath. The products can
be extracted in a suitable solvent, such as ether, and dried. A
mixture of products was identified by .sup.1H and .sup.13C NMR
analysis.
[0120] Analysis indicated that the main products of the nitration
reaction were the 1,2-dinitro compound,
(O.sub.2N)C(R)H--C(R')H(NO.sub.2) and nitro alcohols (e.g. NO.sub.2
. . . OH). It is likely that addition of a nitro radical to the
double bond is followed by reaction of the resulting radical with a
second nitro radical to give the 1,2-dinitroalkane and
1-nitro-2-nitritoalkane. The nitrite group (R--ONO) in the
1-nitro-2-nitrito product tends to undergo hydrolysis during
work-up to give the nitro-alcohol. Only small amounts of
nitroalkene (RCH.dbd.C(R')NO.sub.2) and the allylic nitro products
were observed. The reaction and the resultant mixture of products
is illustrated in Scheme 7 below.
##STR00012##
[0121] Similar reactions were carried out to convert other FAMEs,
e.g. methyl linoleate (methyl cis,cis-9,12-octadecadienoate) and
methyl linolenate (methyl cis,cis,cis-9,12,15-octadecatrienoate) in
chloroform and hexane as solvents.
[0122] Nitration products of abietic acid--the most prevalent of
the organic acids that form the largest constituent of rosin--such
as ethyl abietate were also synthesised in similar fashion.
Reactions were carried out using N.sub.2O.sub.4 in either hexane or
chloroform and a similar mixture of nitrogen-containing products
was formed. Hexane is a preferred solvent for this reaction. The
NMR data was consistent with the formation of dinitro and
nitro-alcohol products containing a single double bond (e.g.
1,4-dinitro-2-alkene).
[0123] DSC/TGA analysis showed that the product mixture underwent
an exothermic decomposition reaction in the temperature range
150-250.degree. C., making a full analysis of the products
difficult.
[0124] Since the relative thermal stability of the organic nitrates
of the invention is one of the key characteristics for determine
(and explain) how rapidly they combust and, hence, how effective
they may be as combustion improvers (cetane number enhancers) when
used in a fuel within a diesel engine, thermal stability assays
(e.g. differential scanning calorimetry/thermogravimetric analysis
(DSC/TGA)) of the products were also conducted, as described in the
Examples. Mass spectrometry (MS) may also be used to provide
information on the decomposition mechanism.
[0125] DSC measures heat flow resulting from evaporation
(endotherm) or thermal decomposition of the compound (exotherm).
TGA measures the weight loss on evaporation or decomposition. MS of
the gas space allows the identity of the volatile decomposition
products to be determined. As well as the decomposition
temperature, the associated exotherm may, in principle, be
determined. These measurements on embodiments of the organic
nitrates according to the invention were intended to provide an
initial assessment of their relative thermal decomposition
behaviour and not limit the scope of the invention.
Diesel Fuel Compositions
[0126] In one aspect of the invention, there is provided a diesel
fuel composition, which comprises an embodiment of a cetane number
improver of the invention. In particular, the cetane number
improver is present at a concentration sufficient and appropriate
for achieving a desired cetane number in the resultant fuel
composition.
[0127] A diesel fuel composition prepared in accordance with
aspects of the present invention may in general be any type of
diesel fuel composition suitable for use in a compression ignition
(diesel) engine; and it may itself comprise a mixture of diesel
fuel components.
[0128] Thus, in addition to the cetane enhancer, a diesel fuel
composition prepared according to aspects of the present invention
may comprise one or more diesel fuel components of conventional
type. It may, for example, include a major proportion of a diesel
base fuel, for instance of the type described below. In this
context, a "major proportion" means at least 50% w/w, and typically
at least 85% w/w based on the overall composition. In a preferred
embodiment, a "major proportion" also includes at least 90% w/w or
at least 95% w/w, and in some cases, at least 98% w/w or at least
99% w/w of the fuel composition consists of the diesel base fuel.
Accordingly, in some embodiments, the base fuel may itself comprise
a mixture of two or more diesel fuel components of the types
described below.
[0129] 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, and are obtained by distillation of a desired range of
fractions from a crude oil. They will typically have boiling points
within the usual diesel range of 150 to 410.degree. C. or 170 to
370.degree. C., depending on grade and use. They will typically
have densities from 0.75 to 0.9 g/cm.sup.3, such as from 0.8 to
0.86 g/cm.sup.3, at 15.degree. C. (IP 365) and measured cetane
numbers (ASTM D613) of from 35 to 80, more preferably from 40 to
75. Their initial boiling points will be in the range 150 to
230.degree. C. and their final boiling points in the range 290 to
400.degree. C. Their kinematic viscosity at 40.degree. C. (ASTM
D445) might suitably be from 1.5 to 4.5 centistokes. Such fuels are
generally suitable for use in compression ignition (diesel)
internal combustion engines, of either the indirect or direct
injection type.
[0130] An automotive diesel fuel composition which results from
carrying out aspects of the present invention also falls within
these general specifications or standards. Accordingly, it will
generally comply with applicable current standard specification(s)
such as for example EN 590 (for Europe) or ASTM D975 (for the USA).
By way of example, the fuel composition may have a density from
0.82 to 0.845 g/cm.sup.3 at 15.degree. C.; a T.sub.95 boiling point
(ASTM D86) of 360.degree. C. or less; a cetane number (ASTM D613)
of 45 or greater; a kinematic viscosity (ASTM D445) from 2 to 4.5
mm.sup.2/s at 40.degree. C.; a sulphur content (ASTM D2622) of 50
mg/kg or less; and/or a polycyclic aromatic hydrocarbons (PAH)
content (IP391 (mod)) of less than 11% w/w. Relevant specifications
may, however, differ from country to country and from year to year
and may depend on the intended use of the fuel composition. In
particular, its measured cetane number will preferably be from 45
to 70, to 75 or to 80, more preferably from 50 to 65, or at least
greater than 50, greater than 55, greater than 60, or greater than
65.
[0131] A petroleum derived gas oil, e.g., obtained from refining
and optionally (hydro)processing a crude petroleum source, may be
incorporated into a diesel fuel composition. 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 hydro-desulphurisation (HDS) unit so as to
reduce their sulphur content to a level suitable for inclusion in a
diesel fuel composition. This also tends to reduce the content of
other polar species such as oxygen- or nitrogen-containing species.
In some cases, the fuel composition will include one or more
cracked products obtained by splitting heavy hydrocarbons.
[0132] In some embodiments of the present invention, the base fuel
may be or contain another so-called "biodiesel" fuel component,
such as a vegetable oil, hydrogenated vegetable oil or vegetable
oil derivative (e.g. a fatty acid ester (FAE), in particular a
fatty acid methyl ester (FAME)), or another oxygenate such as an
acid, ketone or ester. Such components need not necessarily be
bio-derived. Where the fuel composition contains a biodiesel
component, the biodiesel component may be present in quantities up
to 100%, such as between 1% and 99% w/w, between 2% and 80% w/w,
between 2% and 50% w/w, between 3% and 40% w/w, between 4% and 30%
w/w, or between 5% and 20% w/w. In one embodiment, the biodiesel
component may be FAME.
[0133] A diesel base fuel may consist of or comprise a
Fischer-Tropsch derived diesel fuel component, typically a
Fischer-Tropsch derived gas oil. As used herein, the term
"Fischer-Tropsch derived" means that a material is, or is obtained
from, a synthesis product of a Fischer-Tropsch condensation
process. A Fischer-Tropsch derived fuel or fuel component will
therefore be a hydrocarbon stream in which a substantial portion,
except for added hydrogen, is derived directly or indirectly from a
Fischer-Tropsch condensation process.
[0134] Fischer-Tropsch fuels may be derived by converting gas,
biomass or coal to liquid (XtL), specifically by gas to liquid
conversion (GtL), or from biomass to liquid conversion (BtL). Any
form of Fischer-Tropsch derived fuel component may be used as a
base fuel in accordance with aspects of the invention.
[0135] In one embodiment, the base fuel has a low sulphur content,
for example at most 1000 mg/kg (1000 parts per million by
weight/ppmw). In a preferred embodiment, it will have a low or
ultra low sulphur content, for instance at most 500 mg/kg (500
ppmw), such as no more than 350 mg/kg (350 ppmw), and still more
preferably no more than 100 or 50 or 10 or even 5 mg/kg (5 ppmw) of
sulphur. It may be a so-called "zero-sulphur" fuel; although in
some cases it may be desired that the base fuel is not a sulphur
free ("zero sulphur") fuel. In a preferred embodiment, a fuel
composition which results from carrying out aspects of the present
invention will also have a sulphur content falling within these
limits.
[0136] The diesel fuel composition according to aspects of the
present invention may, if desired, contain no, or only low levels
of additional cetane improving (ignition improving) additives such
as 2-ethylhexyl nitrate (2-EHN). In other words, embodiments of the
present invention embrace the use of certain organic nitrates in a
diesel fuel composition for the purpose of reducing the level of a
second (or further) cetane improving additive in the
composition.
[0137] Furthermore, a fuel composition prepared according to
aspects of the present invention, or a base fuel used in such a
composition may contain one or more fuel additives, or may be
additive-free. If additives are included (e.g. added to the fuel at
the refinery), the composition may contain minor amounts of one or
more additives. Selected examples or suitable additives include
(but are not limited to): anti-static agents; pipeline drag
reducers; flow improvers (e.g. ethylene/vinyl acetate copolymers or
acrylate/maleic anhydride copolymers); lubricity enhancing
additives (e.g. ester- and acid-based additives); viscosity
improving additives or viscosity modifiers (e.g. styrene-based
copolymers, zeolites, and high viscosity fuel or oil derivatives);
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); corrosion inhibitors; reodorants;
anti-wear additives; antioxidants (e.g. phenolics such as
2,6-di-tert-butylphenol); metal deactivators; combustion improvers;
static dissipator additives; cold flow improvers (e.g. glycerol
monooleate, di-isodecyl adipate); antioxidants; and wax
anti-settling agents. The composition may for example contain a
detergent. Detergent-containing diesel fuel additives are known and
commercially available. Such additives may be added to diesel fuels
at levels intended to reduce, remove or slow the build up of engine
deposits. In some embodiments, it may be advantageous for the fuel
composition to contain an anti-foaming agent, more preferably in
combination with an anti-rust agent and/or a corrosion inhibitor
and/or a lubricity enhancing additive.
[0138] Where the composition contains such additives (other than
the cetane number increasing components of the invention), it
preferably contains a minor proportion (such as 1% w/w or less,
0.5% w/w or less, 0.2% w/w or less), of the one or more fuel
additives, in addition to the cetane number increasing
component(s). Unless otherwise stated, the (active matter)
concentration of each such additive component in the fuel
composition may be up to 10000 ppmw, such as in the range of 0.1 to
1000 ppmw; and advantageously from 0.1 to 300 ppmw, such as from
0.1 to 150 ppmw.
[0139] If desired, one or more additive components, such as those
listed above, may be co-mixed (e.g. together with suitable diluent)
in an additive concentrate, and the additive concentrate may then
be dispersed into a base fuel or fuel composition. In some cases,
it may be possible and convenient to incorporate the cetane number
increasing component of the invention into such an additive
formulation. Thus, the cetane number improving additive may be
pre-diluted in one or more such fuel components, prior to its
incorporation into the final automotive fuel composition. Such a
fuel additive mixture may typically contains a detergent,
optionally together with other components as described above, and a
diesel fuel-compatible diluent, which may be a mineral oil, a
solvent such as those sold by Shell companies under the trade mark
"SHELLSOL", a polar solvent such as an ester and, in particular, an
alcohol (e.g. hexanol, 2-ethylhexanol, decanol, isotridecanol and
alcohol mixtures such as those sold by Shell companies under the
trade mark "LINEVOL", especially LINEVOL 79 alcohol which is a
mixture of C.sub.7-9 primary alcohols, or a C.sub.12-14 alcohol
mixture which is commercially available).
[0140] In one embodiment, the total content of the additives in the
fuel composition may be between 0 and 10000 ppmw and preferably
below 5000 ppmw.
[0141] As used herein, amounts (e.g. concentrations, ppmw and %
w/w) of components are of active matter, i.e., exclusive of
volatile solvents/diluent materials.
[0142] In one embodiment, the present invention involves adjusting
the cetane number of the fuel composition, using the cetane number
enhancing component, in order to achieve a desired target cetane
number.
[0143] The maximum cetane number of an automotive fuel composition
may often be limited by relevant legal and/or commercial
specifications, such as the European diesel fuel specification EN
590 that stipulates a cetane number of 51. Thus, typical commercial
automotive diesel fuels for use in Europe are currently
manufactured to have cetane numbers of around 51. Thus, embodiments
of the present invention may involve manipulation of an otherwise
standard specification diesel fuel composition, using a cetane
number enhancing additive, to increase its cetane number so as to
improve the combustability of the fuel, and hence reduce engine
emissions and even fuel economy of an engine into which it is, or
is intended to be, introduced.
[0144] In one embodiment, the cetane number improver increases the
cetane number of the fuel composition by at least 3 cetane numbers.
In some particular embodiments, the cetane number increase may be
up to approximately 9, or any value in between these ranges.
Accordingly, in other embodiments, the cetane number of the
resultant fuel is between 51 and 60.
[0145] In a preferred embodiment, an automotive diesel fuel
composition prepared according to aspects of the present invention
will comply with applicable current standard specification(s) such
as, for example, EN 590 (for Europe) or ASTM D-975 (for the USA).
By way of example, the overall fuel composition may have a density
from 820 to 845 kg/m.sup.3 at 15.degree. C. (ASTM D-4052 or EN ISO
3675); a T95 boiling point (ASTM D-86 or EN ISO 3405) of
360.degree. C. or less; a measured cetane number (ASTM D-613) of 51
or greater; a VK 40 (ASTM D-445 or EN ISO 3104) from 2 to 4.5
mm.sup.2/s; a sulphur content (ASTM D-2622 or EN ISO 20846) of 50
mg/kg or less; and/or a polycyclic aromatic hydrocarbons (PAH)
content (IP 391 (mod)) of less than 11% w/w. Relevant
specifications may, however, differ from country to country and
from year to year, and may depend on the intended use of the fuel
composition.
[0146] It will be appreciated, however, that diesel fuel
composition prepared according to aspects of the present invention
may contain fuel components with properties outside of these
ranges, since the properties of an overall blend may differ, often
significantly, from those of its individual constituents.
Uses and Methods
[0147] In accordance with one aspect of the invention, there is
provided the use of an embodiment of the cetane number improver of
the invention to achieve a desired cetane number of the resultant
fuel composition. In some embodiments, the desired cetane number is
achieved or intended to be achieved under a specified set or range
of engine working conditions, as described elsewhere herein.
Accordingly, an advantage of embodiments of the present invention
is that cetane number enhancers of the invention may be suitable
for reducing the combustion delay of a fuel composition under all
engine running conditions, or under mild, or under harsh engine
conditions. Embodiments of the cetane number enhancer of the
invention may serve to improve combustion and, hence, improve
associated engine factors, such as exhaust emissions and/or engine
deposits under a range of engine operating conditions--particularly
under harsh engine conditions when fuel emissions might otherwise
be expected to increase.
[0148] In the context of the present invention, "use" of a cetane
number improver in a fuel composition means incorporating the
component into the composition, typically as a blend (i.e. a
physical mixture) with one or more fuel components (typically
diesel base fuels) and optionally with one or more fuel
additives.
[0149] The cetane number improver is preferably incorporated into
the fuel composition before the composition is introduced into an
engine which is to be run on the composition. Accordingly, the
viscosity increasing component may be dosed directly into (e.g.
blended with) one or more components of the fuel composition or the
base fuel at the refinery. For instance, it may be pre-diluted in a
suitable fuel component, which subsequently forms part of the
overall automotive fuel composition. Alternatively, it may be added
to a diesel fuel composition downstream of the refinery. For
example, it may be added as part of an additive package containing
one or more other fuel additives. This can be particularly
advantageous because in some circumstances it can be inconvenient
or undesirable to modify the fuel composition at the refinery. For
example, the blending of base fuel components may not be feasible
at all locations, whereas the introduction of fuel additives, at
relatively low concentrations, can more readily be achieved at fuel
depots or at other filling points such as road tanker, barge or
train filling points, dispensers, customer tanks and vehicles.
[0150] Accordingly, the "use" of embodiments of the invention may
also encompass the supply of a cetane number improver together with
instructions for its use in a diesel fuel composition to achieve
one of the benefits of the present invention. The cetane number
increasing component may therefore be supplied as a component of a
formulation which is suitable for and/or intended for use as a fuel
additive, in particular a diesel fuel additive. By way of example,
the cetane number improver may be incorporated into an additive
formulation or package along with one or more other fuel additives.
As described above, the one or more fuel additives may be selected
from any useful additive, such as detergents, anti-corrosion
additives, esters, poly-alpha olefins, long chain organic acids,
components containing amine or amide active centres, and any
combination thereof, as is known to the person of skill in the
art.
[0151] According to another aspect of the invention, there is
provided a process for the preparation of an automotive fuel
composition, which process involves blending a diesel base fuel (or
base fuel mixture) with an embodiment of the cetane number improver
of the invention. The blending may be carried out for one or more
of the purposes described herein.
[0152] In some cases the cetane number improver of the invention
may not be suitable for pre-mixing with other fuel additives and
may, therefore, be dosed directly into the fuel composition from a
concentrated (100%) or pre-diluted stock.
[0153] In accordance with one embodiment of the present invention,
two or more cetane number increasing additives may be used in a
diesel fuel composition to provide one or more of the effects of
the invention described herein.
[0154] For example, embodiments of the present invention can
provide an effective way of improving fuel
combustion/combustability in an internal combustion engine.
[0155] It has surprisingly been found that certain organic nitrate
molecules of the invention can, at relatively low concentrations,
increase the cetane number of a diesel fuel composition by an
amount greater than known organic nitrate cetane enhancers under
some engine operating conditions. In particular, embodiments of the
cetance number enhancing agents of the invention may be capable of
providing greater benefits than some prior art cetane number
improvers, particularly under harsh engine working conditions (e.g.
high engine speeds and powers).
[0156] While the amount of the cetane number increasing component
for use in accordance with aspects of the invention may vary
depending of fuel type and/or engine working conditions to be used;
a further benefit of the invention is that under some engine
conditions the amount of cetane number improver needed to observe
the benefit of the invention may be surprisingly low, such as at
the level of typical fuel additives.
[0157] This in turn can reduce the cost and complexity of the fuel
preparation process. For example, it can allow a fuel composition
to be altered in order to improve fuel combustability, by the
incorporation of additives downstream of the refinery, rather than
by altering the content of the base fuel at its point of initial
preparation. The blending of base fuel components may not be
feasible at all locations, whereas the introduction of fuel
additives, at relatively low concentrations, can more readily be
achieved at fuel depots or at other filling points such as road
tanker, barge or train filling points, dispensers, customer tanks
and vehicles. This in particular may be achievable where the cetane
number improver is sufficiently stable to allow it to be
transported under suitable conditions without taking unnecessary
safety risks. Of course, in some case it may not be appropriate due
to safety factors to transport the cetane number improver.
[0158] Moreover, an additive which is to be used at a relatively
low concentration can naturally be transported, stored and
introduced into a fuel composition more cost effectively than can a
fuel component which needs to be used at concentrations of the
order of tens of percent by weight.
[0159] Another aspect of the invention provides a method of
operating an internal combustion engine and/or a vehicle powered by
such an engine, which comprises introducing into a combustion
chamber of the engine a fuel composition prepared in accordance
with aspects of the invention. The fuel composition is
advantageously introduced for one or more of the purposes described
in connection with aspects of this invention. Thus, the engine is
preferably operated with the fuel composition for the purpose of
improving ease of fuel ignition during use of the engine (by
increasing fuel combustability) and, for example, associated
benefits such as reduced engine emissions, engine noise, etc. The
engine is in particular a diesel engine, and may be a turbo charged
diesel engine. The diesel engine may be of the direct injection
type, for example of the rotary pump, in-line pump, unit pump,
electronic unit injector or common rail type, or of the indirect
injection type. It may be a heavy or a light duty diesel engine.
For example, it may be an electronic unit direct injection (EUDI)
engine.
[0160] Where relevant to a particular assessment, emission levels
may be measured using standard testing procedures such as the
European R49, ESC, OICA or ETC (for heavy-duty engines) or ECE+EUDC
or MVEG (for light-duty engines) test cycles. In a preferred
embodiment, emissions performance is measured on a diesel engine
built to comply with the Euro II standard emissions limits (1996)
or with the Euro III (2000), IV (2005) or even V (2008) standard
limits.
[0161] Throughout the description and claims of this specification,
the singular encompasses the plural unless the context otherwise
requires. In particular, where the indefinite article is used, the
specification is to be understood as contemplating plurality as
well as singularity, unless the context requires otherwise.
[0162] Thus features, integers, characteristics, compounds,
chemical moieties or groups described in conjunction with a
particular aspect, embodiment or example of the present invention
are to be understood to be applicable to any other aspect,
embodiment or example described herein unless incompatible
therewith. Thus, features of the "uses" of the invention are
directly applicable to the "methods" of the invention. Moreover,
unless stated otherwise, any feature disclosed herein may be
replaced by an alternative feature serving the same or a similar
purpose.
[0163] Aspects of the invention will now be further illustrated by
way of the following non-limiting examples.
EXAMPLES
Introduction
[0164] Various organic nitrates were synthesised and assayed for
their potential to act as cetane enhancers in diesel fuels. Cetane
enhancers of the invention may provide various benefits, in use,
that are associated with increased combustability and a reduction
in ignition delay, such as reducing engine noise, reducing build-up
of engine deposits, reducing engine emissions, and may even improve
fuel economy in some cases.
[0165] Organic nitrates of the invention were also tested for
thermal stability to obtain useful information on necessary storage
and transportation conditions.
[0166] Organic nitrate synthesis processes may also help in
determining suitability of the organic nitrates for use as cetane
enhancers in diesel fuel at a commercial level (e.g. with respect
to ease of synthesis and cost of production).
Reagents and Chemicals
[0167] In general, standard reagents, chemicals and solvents were
purchased from Sigma-Aldrich. Ethyl abietate (70%) was obtained
from TCI and ABCR. Methyl linoleate was purchased from TCI. Neodol
23 (C12-C13 alcohol mixture) was obtained from Shell Chemicals.
[0168] To form the solution of N.sub.2O.sub.4, gaseous yellow/brown
NO.sub.2/N.sub.2O.sub.4 (Sigma-Aldrich) was slowly bubbled into the
solvent (chloroform or hexane) in a round-bottomed-flask in an ice
bath. The dew point of the N.sub.2O.sub.4 is around 20.degree. C.,
so the heavy gas condenses into the cold solvent (at ca. 4.degree.
C.). The amount of N.sub.2O.sub.4 added was determined by weighing
the flask before and after addition of N.sub.2O.sub.4.
General
[0169] The following general synthesis methods were used for the
preparation of nitrate and nitro compounds of the invention:
[0170] Nitric acid, for secondary alcohols
[0171] Mixture of nitric acid, sulfuric acid and urea, for primary
or secondary alcohols
[0172] Mixture of nitric acid and acetic anhydride (precursor of
reactive acetyl nitrate) in acetic acid, for unsaturated
alcohols
[0173] N.sub.2O.sub.4, for olefins
[0174] A 500 ml three-necked round-bottomed flask, equipped with a
`bubbler`, thermometer, a dropping funnel and a magnetic stirring
bar was used in all the experiments. Reactions were performed under
nitrogen.
Synthesis of Organic Nitrates
Nitration Product of 1-Octanol
##STR00013##
[0176] A mixture of concentrated nitric acid (45 ml, 0.96 mol),
concentrated sulfuric acid (134 ml, 2.35 mol) and urea (5 g, 0.08
mol) were placed in a 500 m three-necked flask and cooled to
0.degree. C. 1-Octanol (48 ml, 0.30 mol) in dichloromethane (30 ml)
was added from a dropping funnel for 60 min. The temperature was
maintained at 0 to 5.degree. C. with an ice-salt bath. After 2
hours the reaction mixture was poured in an ice bath (quenched) and
dichloromethane (100 ml) was added. The organic phase was washed
for three times with water, followed by sodium bicarbonate. The
organic phase was dried over magnesium sulfate and the solvent was
evaporated by a rotorvap (40.degree. C. bath temperature, 5 mbar
vacuum). The yield was 43 g (81%).
[0177] .sup.1H NMR (CDCl.sub.3, 300 MHz): 4.4 (t, 2H), 1.8-1.6 (m,
2H), 1.4-1.1 (m, 10H), 0.9-0.8 (m, 3H)
[0178] .sup.13C NMR (CDCl.sub.3): 73.7, 32.0, 29.5, 29.4, 27.1,
26.0, 23.0, 14.4
Nitration Product of 1,10-Decanediol
##STR00014##
[0180] A mixture of concentrated nitric acid (67 ml, 1.44 mol),
concentrated sulfuric acid (200 ml, 3.50 mol) and urea (7 g, 0.12
mol) were placed in a 500 ml three-necked flask and cooled to
0.degree. C. 1,10-octanediol (48 ml, 0.30 mol) in dichloromethane
(30 ml) was added from a dropping funnel for 60 min. The
temperature was maintained at 0 to 5.degree. C. with an ice-salt
bath. After 2 hours the reaction mixture was poured in an ice bath
(quenched) and dichloromethane (100 ml) was added. The organic
phase was washed for three times with water, followed by sodium
bicarbonate. The organic phase was dried over magnesium sulfate and
the solvent was evaporated by a rotorvap (40.degree. C. bath
temperature, 5 mbar vacuum). The yield was 49 g (98%).
[0181] .sup.1H NMR (CDCl.sub.3, 300 MHz): 4.4 (t, 4H), 1.8-1.6 (m,
4H), 1.4-1.2 (m, 12H)
[0182] .sup.13C NMR (CDCl.sub.3): 73.7, 29.5, 29.3, 27.0, 25.9
Nitration Product of 1-Tetradecanol
##STR00015##
[0184] A mixture of concentrated nitric acid (27 ml, 0.58 mol),
concentrated sulfuric acid (81 ml, 1.42 mol) and urea (3 g, 0.05
mol) were placed in a 500 ml three-necked flask and cooled to
0.degree. C. 1-Tetradecanol (48 ml, 0.19 mol) in dichloromethane
(30 ml) was added from a dropping funnel for 45 min. The
temperature was maintained at 0 to 5.degree. C. with an ice-salt
bath After 2 hours the reaction mixture was poured in an ice bath
(quenched) and dichloromethane (100 ml) was added. The organic
phase was washed for three times with water, followed by sodium
bicarbonate. The organic phase was dried over magnesium sulfate and
the solvent was evaporated by a rotorvap (40.degree. C. bath
temperature, 5 mbar vacuum). The yield was 38 g (79%).
[0185] .sup.1H NMR (CDCl.sub.3, 300 MHz): 4.4 (t, 2H), 1.8-1.6 (m,
2H), 1.5-1.2 (m, 22H), 0.9-0.8 (m, 3H)
[0186] .sup.13C NMR (CDCl.sub.3): 73.7, 32.3, 30.0, 29.9, 29.8,
29.7, 29.5, 26.0, 23.1, 14.5
Nitration Product of Hexadecyl Alcohol
##STR00016##
[0188] A mixture of concentrated nitric acid (24 ml, 0.52 mol),
concentrated sulfuric acid (72 ml, 1.26 mol) and urea (2 g, 0.04
mol) were placed in a 500 ml three-necked flask and cooled to
0.degree. C. Hexadecyl alcohol (40 g, 0.16 mol) in dichloromethane
(30 ml) was added from a dropping funnel for 60 min. The
temperature was maintained at 0 to 5.degree. C. with an ice-salt
bath. After 2 hours the reaction mixture was poured in an ice bath
(quenched) and dichloromethane (100 ml) was added. The organic
phase was washed for three times with water, followed by sodium
bicarbonate. The organic phase was dried over magnesium sulfate and
the solvent was evaporated by a rotorvap (40.degree. C. bath
temperature, 5 mbar vacuum). The yield was 39 g (80%).
[0189] .sup.1H NMR (CDCl.sub.3, 300 MHz): 4.5 (t, 2H), 1.8-1.6 (m,
2H), 1.4-1.2 (m, 26H), 0.9-0.8 (m, 3H)
[0190] .sup.13C NMR (CDCl.sub.3): 73.6, 32.3, 30.1, 29.8, 27.0,
26.0, 23.1, 14.5
Nitration Product of 1-Octadecanol
##STR00017##
[0192] A mixture of concentrated nitric acid (16 ml, 0.35 mol),
concentrated sulfuric acid (48 ml, 0.85 mol) and urea (2 g, 0.03
mol) were placed in a 500 ml three-necked flask and cooled to
0.degree. C. 1-Octadecanol (36 g, 0.11 mol) in dichloromethane (30
ml) was added from a dropping funnel for 60 min. The temperature
was maintained at 0 to 5.degree. C. with an ice-salt bath. After 2
hours the reaction mixture was poured in an ice bath (quenched) and
dichloromethane (100 ml) was added. The organic phase was washed
for three times with water, followed by sodium bicarbonate. The
organic phase was dried over magnesium sulfate and the solvent was
evaporated by a rotorvap (40.degree. C. bath temperature, 5 mbar
vacuum). The yield was 28 g (80%).
[0193] .sup.1H NMR (CDCl.sub.3, 300 MHz): 4.5 (t, 2H), 1.8-1.6 (m,
2H), 1.4-1.2 (m, 30H), 0.9-0.8 (m, 3H)
[0194] .sup.13C NMR (CDCl.sub.3): 73.7, 32.3, 30.1, 30.0, 29.9,
29.7, 29.5, 27.1, 26.0, 23.1, 14.5
Nitration Product of Neodol 23
[0195] A mixture of concentrated nitric acid (31 ml, 0.66 mol),
concentrated sulfuric acid (92 ml, 1.61 mol) and urea (3 g, 0.05
mol) were placed in a 500 ml three-necked flask and cooled to
0.degree. C. Neodol 23 (48 ml, 0.21 mol) in dichloromethane (30 ml)
was added from a dropping funnel for 60 min. The temperature was
maintained at 0 to 5.degree. C. with an ice-salt bath. After 2
hours the reaction mixture was poured in an ice bath (quenched) and
dichloromethane (100 ml) was added. The organic phase was washed
for three times with water, followed by sodium bicarbonate. The
organic phase was dried over magnesium sulfate and the solvent was
evaporated by a rotorvap (40.degree. C. bath temperature, 5 mbar
vacuum). A mixture of dodecyl and tridecyl nitrates was obtained
with a yield of 45 g (93%).
[0196] .sup.1H NMR (CDCl.sub.3, 300 MHz): 4.5 (t, 2H), 1.8-1.6 (m,
2H), 1.4-1.2 (m, 16H), 0.9-0.8 (m, 3H)
[0197] .sup.13C NMR (CDCl.sub.3): 73.7, 32.3, 30.0, 29.9, 29.7,
29.5, 27.1, 26.0, 23.1, 14.5
Nitration Product of Exo-Borneol
##STR00018##
[0199] In a 500 ml three neck-flask filled with nitric acid (150.21
ml, 3.24 mol) was added exo-borneol (50 g, 0.32 mol) slowly (3.5
hours) at room temperature. After 2 hours the reaction mixture was
poured in an ice bath (quenched) and diethyl ether (200 ml) was
added. The organic phase was washed for three times with water,
followed by sodium bicarbonate. The organic phase was dried over
magnesium sulfate and was the solvent was evaporated by a rotorvap,
40.degree. C. bath temperature and .+-.5 mbar vacuum. The yield was
57 g (87%).
[0200] .sup.1H NMR (CDCl.sub.3, 300 MHz): 4.8 (t, 1H), 2.0-1.9 (m,
2H), 1.8-1.6 (m, 3H), 1.3-1.1 (m, 2H), 1.0-0.9 (m, 6H), 0.8 (s,
3H)
[0201] .sup.13C NMR (CDCl.sub.3): 90.5, 49.9, 47.4, 45.1 38.3,
34.5, 27.2, 20.2, 11.5
Nitration Product of Exo-Fenchol
##STR00019##
[0203] In a 500 ml three neck-flask was filled L-Fenchone (40 g,
0.26 mol), aluminium isopropoxide (2 g) and isopropyl alcohol (300
ml). This mixture was refluxed (during reflux the acetone was
evaporated and filled with isopropyl alcohol) for 168 hours,
extracted with diethyl ether, dried and evaporated. 25 g
exolendo-fenchol in ratio 3:1 was isolated.
[0204] In a 500 ml three neck-flask filled with nitric acid (75.10
ml, 1.62 mol) was added the exo/endofenchol mixture (25 g, 0.16
mol) slowly (2 hours) at room temperature. After 2 hours the
reaction mixture was poured in an ice bath (quenched) and diethyl
ether (100 ml) was added. The organic phase was washed for three
times with water, followed by sodium bicarbonate. The organic phase
was dried over magnesium sulfate and the solvent was evaporated
using a rotorvap, 40.degree. C. bath temperature and .+-.5 mbar
vacuum. The yield was 26 g (82%).
[0205] .sup.1H NMR (CDCl.sub.3, 300 MHz): 4.8-4.6 (m, 1H), 4.2-4.2
(m, 1H), ratio 1:0.47
[0206] .sup.13C NMR (CDCl.sub.3): 97.2, 88.2
Nitration Product of L-Menthol
##STR00020##
[0208] A mixture of concentrated nitric acid (15.79 ml, 0.34 mol),
concentrated sulphuric acid (47.37 ml, 0.83 mol) and urea (1.62 g,
0.03 mol) were placed in a 500 ml three necked flask and cooled to
0.degree. C. L-menthol (17 g, 0.11 mol) in diethyl ether (20 ml)
was added from a dropping funnel for 60 min. The temperature was
maintained at 0 to 5.degree. C. with an ice-salt bath. After 2
hours the reaction mixture was poured in an ice bath (quenched) and
diethyl ether (100 ml) was added. The organic phase was washed for
three times with water, followed by sodium bicarbonate. The organic
phase was dried over magnesium sulfate and was the solvent was
evaporated by a rotorvap, 40.degree. C. bath temperature and .+-.5
mbar vacuum. The yield was 41 g (95%).
[0209] .sup.1H NMR (CDCl.sub.3, 300 MHz): 4.9-4.8 (m, 1H), 2.2-1.9
(m, 2H), 1.8-1.7 (m, 2H), 1.6-1.4 (m, 2H), 1.2-1.0
[0210] (m, 2H), 1.0-0.9 (m, 6H), 0.9-0.8 (m, 3H)
[0211] .sup.13C NMR (CDCl.sub.3): 84.4, 45.8, 39.7, 34.2, 31.8,
26.5, 24.2, 22.2, 20.8, 16.8
Nitration Product of Oleyl Alcohol
##STR00021##
[0213] To a mixture of acetic anhydride (80 mL), acetic acid (80
ml) and oleyl alcohol (40 g) at 15.degree. C., was added nitric
acid (10 ml) drop wise (60 min). After 30 min the reaction mixture
was poured in an ice bath (quenched) and diethyl ether (100 ml) was
added. The organic phase was washed for three times with water,
followed by sodium bicarbonate. The organic phase was dried over
magnesium sulfate and was the solvent was evaporated by a rotorvap,
40.degree. C. bath temperature and .+-.5 mbar vacuum. The yield was
34 g (74%).
[0214] .sup.1H NMR (CDCl.sub.3, 300 MHz): 5.4-5.2 (m, 2H), 4.4 (t,
2H), 2.1-1.9 (m, 4H), 1.4-1.2 (24H), 1.0-0.8 (m, 3H)
[0215] .sup.13C NMR (CDCl.sub.3): 130.2, 129.8, 73.7, 32.3, 30.1,
30.0, 29.9, 29.7, 29.6, 29.5, 29.4, 27.6, 27.5, 27.1, 26.0, 23.1,
14.5
Nitration Product of Cholesterol
##STR00022##
[0217] To a mixture of cholesterol (35 g) in chloroform (10 ml) and
acetic anhydride (90 ml) in chloroform (10 ml) at 15.degree. C.,
was added drop wise (60 min) a mixture of nitric acid (12.6 ml) in
acetic acid (45 ml). After 60 min the reaction mixture was poured
in an ice bath (quenched) and diethyl ether (100 ml) was added. The
organic phase was washed for three times with water, followed by
sodium bicarbonate. The organic phase was dried over magnesium
sulfate and was the solvent was evaporated by a rotorvap,
40.degree. C. bath temperature and .+-.5 mbar vacuum. The yield was
24 g (63%). Cholesterol nitrate is a solid at RT.
[0218] .sup.1H NMR (CDCl.sub.3, 300 MHz): 5.5-5.4 (m, 1H), 4.9-4.7
(m, 1H), 2.6-2.3 (m, 2H), 2.1-1.1 (m, 25H), 1.1-0.9 (m, 15H),
0.8-0.6 (m, 3H)
[0219] .sup.13C NMR (CDCl.sub.3): 138.3, 122.3, 83.5, 57.6, 56.5,
50.2, 42.5, 40.2, 40.1, 37.8, 37.5, 31.8, 29.5, 26.8, 23.4, 18.5,
17.5, 11.2
Nitration Product of Methyl Oleate
[0220] To a solution of N.sub.2O.sub.4 (13.96 g, 0.15 mol) in
chloroform (20 ml) at 0.degree. C. was added drop wise (3 hours)
methyl oleate (30 g, 34.48 ml). The reaction mixture was stirred
for 48 hours with a low nitrogen flow. The reaction mixture was
poured in an ice bath (quenched) and diethyl ether (50 ml) was
added. The organic phase was washed for three times with water. The
organic phase was dried over magnesium sulfate and was the solvent
was evaporated by a rotorvap, 40.degree. C. bath temperature and
.+-.5 mbar vacuum. The yield was 31.2 g.
Nitration Product of Ethyl Abietate
[0221] To a solution of N.sub.2O.sub.4 (12.75 g, 0.14 mol) in
hexane (20 ml) at 0.degree. C. was added drop wise (2 hours) ethyl
abietate (30 g, 34.48 ml). The reaction mixture was stirred for 48
hours with a low nitrogen flow. The reaction mixture was poured in
an ice bath (quenched) and diethyl ether (50 ml) was added. The
organic phase was washed for three times with water. The organic
phase was dried over magnesium sulfate and was the solvent was
evaporated by a rotorvap, 40.degree. C. bath temperature and .+-.5
mbar vacuum. The yield was 33.2 g. The products of the reaction are
solid at RT.
Analytical Methods
[0222] .sup.1H and .sup.13C NMR spectra were recorded on a Varian
Mercury 300 MHz or a Varian Inova 400 MHz system. All NMR samples
were measured in CDCl.sub.3.
[0223] Infrared spectra were measured on a Nicolet 6700 FT-IR
Spectrometer (Fourier transform infrared spectroscopy) from Thermo
Scientific.
[0224] Gas chromatography-mass spectrometry (GC-MS) analyses were
performed on a Trace GC Ultra chromatograph from Interscience
equipped with a 50 m.times.0.2 mm.times.0.5 .mu.m RTX-1 PONA column
and an DSQII mass-selective EI detector. The following temperature
profile was used in the GC-MS for measuring the components. The
oven started at 35.degree. C. for the first 5 min, then increased
with 10.degree. C./min to 300.degree. C. followed by a hold time of
10 min at 300.degree. C. DSC/TGA was measured on a STA 409 PC
(Simultaneous Thermal Analysis) with QMS 403 C (quadrupole mass
spectrometers) from NETZSCH.
Testing of Blended Fuels
[0225] The organic nitrate (or nitro) cetane number enhancing
agents were performance tested in diesel fuel blends. The
assessment of their ability to increase the cetane number of the
fuel was carried out indirectly by measuring changes in ignition
delay (ID) of the blended fuels using a combustion research unit
(CRU). The CRU is operated to determine ignition quality in a
similar fashion to the ignition quality tester (IQT; International
Standard EN 15195:2007:E) known to the person of skill in the art,
i.e. using a heated, pressurised constant volume chamber.
Typically, the cetane number is given as a dimensionless number,
which describes the ignition behaviour of a fuel in comparison to
primary reference fuels (PRFs) with a defined cetane number. PRFs
are bimodal mixtures of n-hexadecane (or "cetane"; CN=100) and
heptamethylnonane (CN=15).
Fuel Blending
[0226] All test compounds were blended into an EN590 compliant
diesel (European specification), zero-sulfur fuel (i.e. ZSD
base-fuel from Stanlow refinery; density 837.4 kg/m.sup.3 at
15.degree. C.; viscosity 2.89 mm.sup.2/s at 40.degree. C.) at
concentrations of 0.1% w/w and 1.0% w/w. Some test compounds were
also blended at concentrations of 0.05% w/w and 0.5% w/w. The
mixtures were stirred at RT for 1 hour, after which all solid
compounds were dissolved in the base fuel.
[0227] For purposes of comparison, similar fuel blends containing
2-EHN were prepared.
Combustion Research Unit (CRU) Testing
[0228] In CRU tests, diesel-like fuel is injected into a high
temperature, high pressure chamber where it mixes with the hot air
and ignites, thus mimicking combustion in a compression-ignition
engine. The combustion process is monitored via a pressure sensor
inside the chamber.
[0229] The CRU delivers p-t-charts of the ignition process from
which the ignition delay, the burn rate and the maximum pressure
increase (MPI) can be determined. A comparison of blended fuels
with standard fuels demonstrates changes in ignition
delay/combustability of the fuels, and may also allow determination
of cetane numbers under different operating conditions.
[0230] The engine conditions selected for CRU tests are designed to
simulate a wide range of engine operating conditions so as to
assess the cetane enhancers under mild, intermediate and harsh
conditions; e.g. temperature and pressure are both varied from low
to high. This allows the temperature and pressure dependence of
ignition delay to be demonstrated. Thus, the slope of the
isothermal or isobaric charts plotted from the data obtained from
these tests provide direct information about how the response of
the fuel blend changes from mild to harsh conditions.
[0231] Each of the fuel blends (at each concentration of cetane
enhancer used) and the base fuels were tested for ignition quality
on the CRU under the 11 different sets of parameters (engine
operating conditions) illustrated in Table 1.
TABLE-US-00001 TABLE 1 Conditions 01 to 11 used for CRU
measurements of fuel blends. Delay Pre- p.sub.Chamb/ Main bar
Pre-Inj. Main Inj. (usec) Working T.sub.Wall/.degree. C. range
p.sub.Fuel/bar Period/ Period/usec range EGR/% point range 350-590
10-75 range 200-1600 usec 0-1400 range 100-1500 100-3000 range
0-100 No. Injections 01 590 30 900 0 900 100 0 10 02 590 50 900 0
900 100 0 10 03 590 75 900 0 900 100 0 10 04 560 30 900 0 900 100 0
10 05 560 50 900 0 900 100 0 10 06 560 75 900 0 900 100 0 10 07 530
30 900 0 900 100 0 10 08 570 21.4 200 0 1500 100 0 10 09 530 75 900
0 900 100 0 10 10 530 50 900 0 900 100 0 10 11 590 65 1600 0 1500
100 0 10
Ignition Delay
[0232] The primary data obtained from CRU measurements are
pressure-time traces, from which the ignition delay (ID), burn
period (BP) and maximum pressure increase (MPI) can be
determined.
[0233] There are different definitions for ignition delay.
Typically, ID.sup.5% or ID.sup.0.2 measurements are used, which are
defined as the time taken for the pressure in the combustion
chamber to rise to its initial value plus 5% of the MPI, or to 0.2
bar above its initial value, respectively. In these studies both
values are used, although ID.sup.0.2 is preferred due to the lower
standard deviations observed.
[0234] A derived ignition quality (DIQ) is obtained from the
ignition delay via comparison with primary reference fuels (PRFs),
which have a known cetane number. Since ignition delay correlates
with the cetane number of the fuel, a calibration model can be
obtained for all conditions. With such calibrations, DIQ can be
determined for any unknown fuel and derived as a pseudo-cetane
number.
[0235] The PRFs used in this study are shown in Table 2.
TABLE-US-00002 TABLE 2 PRFs used to determine the ID-DIQ
calibration models. PRF Cetane Heptamethylnonane CN number (Vol %)
(Vol %) (by definition) 1 40.0 60.0 49 2 100.0 0.0 100 3 64.7 35.3
70 4 88.2 11.8 90 5 52.9 47.1 60 6 76.5 23.5 80 7 35.3 64.7 45
[0236] The effect of the different organic nitrates in fuel blends
was compared by measuring ignition delay and calculating the
percentage ID-reduction relative to the respective base fuel. The
results for exemplary combustion conditions 03, 05, 07 and 08 are
illustrated in FIG. 2.
[0237] The graphs show the data obtained at organic nitrate
concentrations of 1.0% w/w (left, graphs A, C, E and G) and 0.1%
w/w (right, graphs B, D, F and H) at representative combustion
conditions (first row, condition a03, graphs A and B; second row,
condition a05, graphs C and D; third row, condition a07, graphs E
and F; and fourth row, condition a08, graphs G and H). Data for
organic nitrates is as follows: exo bornyl nitrate (column 1);
menthly nitrate (column 2); oleyl nitrate (column 3); 1,10-decyl
dinitrate (column 4); 1-octadecyl nitrate (column 5);
nitro-substituted methyl oleate (column 6); cholesterol nitrate
(column 7); 1-octyl nitrate (column 8); 1-tetradecyl nitrate
(column 9); 2-ethylhexyl nitrate (positive control, column 10);
1-hexadecyl nitrate (column 11); dodecyl/tridecyl nitrate mixture
(column 12); nitro-substituted ethyl abietate (column 13); and exo
fenchyl nitrate (column 14)
[0238] These data show that all of the organic nitrates provided a
benefit compared to the base fuel by achieving a shorter ignition
delay. In general, menthyl nitrate achieved a greater reduction in
ignition delay than the known cetane enhancer, 2-EHN, under all
test conditions, and was the most effective combustion enhancer
tested. Under some test conditions exo-fenchyl nitrate or
1,10-decyl dinitrate gave the greatest reductions in ignition
delay. In general, 1,10-decyl dinitrate, neodo123 nitrate (mixture
of dodecyl and tridecyl nitrates), and 1-octyl nitrate achieved
similar reductions in ignition delay to 2-EHN under all test
conditions. Some organic nitrates displayed a
concentration-dependent effect. For example, exo-fenchyl nitrate
was generally the most effective cetane enhancer at low
concentrations (e.g. 0.1% w/), while it was generally slightly less
effective than menthyl nitrate at higher concentrations (e.g. 1.0%
w/w). Furthermore, the effect was most pronounced under the milder
test conditions. Interestingly, the fatty acid derived nitrates
displayed slight reductions in effectiveness as chain length
increased. Of the saturated and unsaturated nitrates of the same
carbon-chain length, it appears that the saturated nitrates provide
a stronger cetane boost than unsaturated molecules. The results
also suggest that the nitrated molecules are more effective cetane
enhancers than the nitro molecules.
Dose Rate Response
[0239] The effectiveness of the terpene nitrates, exo-bornyl
nitrate and L-menthyl nitrate, were tested at different dose levels
(i.e. 0.05% w/w, 0.1% w/w, 0.5% w/w and 1.0% w/w). The results (not
shown) illustrate that there is a saturation effect for cetane
enhancement. Thus, at the low concentrations tested (0.05% w/w and
0.1% w/w) there was a clear concentration-dependent reduction in
ignition delay. However, a relatively small additional reduction in
ignition delay was observed in the concentration range of 0.1% w/w
to 0.5% w/w and 1.0% w/w. This saturation effect was found under
all combustion conditions tested.
[0240] Importantly, therefore, the effective additives can be used
to good effect at low concentrations, which is useful in many
respects, such as production level, storage, cost, handling and
safety.
Derived Ignition Quality (DIQ)
[0241] The derived ignition quality (DIQ) was determined for each
of the organic nitrates at concentrations of 0.1% w/w and 1.0%
w/w.
[0242] By way of example, the DIQ for the diesel base fuel
comprising exo-fenchyl nitrate at different concentrations (i.e.
0.1% w/w and 1.0% w/w) was determined relative to the non-modified
base fuel composition and relative to blends with the known cetane
enhancer, 2-EHN. Studies were carried out under all 11 sets of
combustion conditions and the results are shown in FIG. 3. The left
graph shows the results of a base fuel containing exo-fenchol
nitrate at concentration of 0.1% w/w, and the right graph shows the
results for concentration of 1.0% w/w, measured under all test
combustion conditions, a01 to a08 (columns 1 to 8, respectively)
and a09 to all (columns 10 to 12, respectively). In each graph, for
comparative purposes the DIQ of the diesel base fuel under reaction
condition a08 is illustrated (column 9);
[0243] By way of example, these data show that at IQT-conditions
08, as specified in cetane number measurement according to EN15195
(Oxley et al. (2000) Energy Fuels, 14, 1252-1264), the 0.1% w/w
exo-fenchyl nitrate fuel blend achieved a DIQ of 52.2, while the
1.0% w/w exo-fenchyl nitrate fuel blend had a DIQ of 63.7. This
represents a significant increase on the DIQ of 44.1 for the base
fuel composition alone. These results thus show a cetane number
enhancement of 7.1 at 1000 ppm, which is similar to that expected
for 2-EHN.
Isothermal and Isobaric Response
[0244] The isothermal and isobaric responses of the fuel blends
were measured and compared to see the effect of temperature and
pressure on ignition delay for each organic nitrate. In particular,
the experimental design that was chosen for CRU measurements
allowed for isobaric and isothermal comparison of the additives,
which provided an opportunity to follow the response of additives
as combustion conditions changed from mild to harsh.
[0245] The data, not illustrated, demonstrated that in general all
additives showed the same response pattern irrespective of their
specific performance as ignition enhancers. Higher temperature and
higher pressure (harsh conditions) resulted in reduced ignition
delays (i.e. each additive demonstrated a parallel down-shift
compared to the base fuel as pressure and/or temperature increased.
Thus, under combustion condition 11 (maximum power), typically, the
ignition delay was the shortest. This may be due to faster
injection rate and mixing. However, it was found that the relative
difference in ignition delay in comparison to the base fuel
increased with reducing temperature. In other words, relative to
base fuel the reduction in ignition delay is greater at mild
conditions.
Thermal Stability
[0246] Differential scanning calorimetry/thermogravimetric analysis
(DSC/TGA) was used to evaluate the thermal stabilities of the
nitrates and other compounds prepared in the study; and also to
provide information on the decomposition mechanism from mass
spectrometry (MS) of the volatile products.
[0247] The experiments were carried out under argon flow, with a
temperature profile of 5.degree. C./min up to 200-350.degree. C.
Assays were carried out under atmospheric pressure and, hence, the
thermal degradation of products that evaporate prior to thermal
decomposition could not be studied (e.g. 1-octyl nitrate).
[0248] An exemplary DSC/TGA assay trace for 1,10-decyl dinitrate is
illustrated in FIG. 5. As illustrated, the product begins to
decompose at a temperature of approximately 170.degree. C. The line
beginning in the top left of the graph illustrates the weight loss
of the product on decomposition. The two traces showing sharp peaks
towards the right hand side of the graph represent the exotherm
(right-hand peak: maximum at about 200.degree. C.) and the
concentration of the decomposition product (left-hand peak).
[0249] Typically several ions are observed in MS studies of the
organic nitrates under thermal decomposition (e.g. M (or M/2)=12,
14, 18, 28, 30, 44, 46 and 56).
[0250] Without wishing to be bound by theory, the rate-determining
step in the decomposition of primary and secondary nitrates is
thought to be the homolysis of the RO--NO.sub.2 bond to give the
alkoxyl radical and NO.sub.2. This may be followed by one or more
competing reactions of the alkoxyl radical, e.g.: 13-cleavage of
the alkoxyl radical to liberate formaldehyde (CH.sub.2O) and form
an alkyl radical, which may undergo .beta.-cleavage or other
reaction; loss of a hydrogen radical (via the alternative-cleavage)
to give an anhydride; and hydrogen abstraction from a suitable
hydrogen donor (e.g. PhCH.sub.2R) to give the alcohol.
[0251] The degradation mechanism and product distribution for a
particular nitrate depends on whether it occurs in the liquid or
gas phase and the presence of other components. Without being bound
by theory, it is expected that the compound 1,10-decyl dinitrate
would decompose in a similar fashion to the mononitrates, except
perhaps, more quickly as the two nitrate functionalities are
effectively isolated.
[0252] The DSC/TGA method was initially used to confirm that
product samples were sufficiently stable to allow safe
transportation and storage. However, the methods also provide
detailed information on the thermal degradation of potential cetane
enhancers, including on the mechanism of decomposition, at least
for those products that do not (partially) evaporate below the
degradation temperature (linear organic nitrates having less than
14 carbon atoms may require a modified method).
[0253] The DSC method provides some qualitative information on the
relative stability of different cetane enhancers, but, as it
involves a temperature scan, it does not directly reflect the
relative thermal stability at any particular temperature. Hence,
the stability order derived from the temperature of exotherm
maximum may differ from that determined at a particular temperature
in kinetic experiments if the activation energy of the compounds
differs. Components exhibiting a broad exotherm would be expected
to have a lower activation energy than those with a narrow
exotherm.
[0254] Methods are known for determining kinetic parameters from
single scan DSC heat flow data, from the dependence of the
temperature of maximum exotherm on the heating rate, and using
isothermal DSC methods. For example, the activation energy and
pre-exponential factor for the decomposition of di-t-butylperoxide
have been determined from DSC. It should, in principle, be possible
(e.g. using adiabatic measurements) to extend these methods for the
determination of Arrhenius kinetic constants to cetane enhancers
based on organic nitrates and related compounds.
[0255] The identification of more stable cetane enhancers is an
attractive prospect as it may then be possible to transport and
supply such cetane enhancers in more concentrated stocks than is
possible for the current commonly used cetane enhancers, such as
2-EHN. This may then provide a number of advantages over existing
formulations, such as by reducing the volume of chemicals that need
to be added to fuels and, thus, transported and stored. It may also
reduce or eliminate the need for some specialist storage,
transportation and/or handling equipment to avoid combustion
hazards. While the organic nitrates of the invention in general are
more stable than some known cetane enhancers (e.g.
Di-tert-butylperoxide, DTBP), tetradecyl nitrate is a particularly
attractive cetane enhancer of the invention that appears to be more
stable than 2-EHN.
Adiabatic Thermal Stability Measurements
[0256] To obtain a quantitative measurement of the thermal
stability of some cetane enhancers adiabatic heat-wait search (HWS)
experiments were carried out using a Phi-Tech calorimeter, which
gives an accurate determination of kinetic and thermodynamic
parameters of the molecules decomposition reaction.
[0257] The Phi-Tec equipment is usually operated in a
heat-wait-search mode, which means that the temperature of the
reactor is increased stepwise until the decomposition onset
temperature (DOT) of the reaction is detected. Onset temperatures
are graphically derived by searching for the temperature at which
deviation from linear temperature rise takes place due to
self-heating of the sample. The apparatus than automatically tracks
the runaway exotherm to 490.degree. C. maximum (at short exposure
time; otherwise 400.degree. C.). The decomposition onset is
detected when the self heating rate exceeds 0.02.degree.
C./min.
[0258] Typical Phi-Tec reaction conditions:
Intake sample: ca. 66 g; Test cell material: SS-316 (STRCA type,
1*1/8'' tube connection); Void cell volume: ca. 110 ml; Start
temperature: ca 20.degree. C. below T.sub.onset (ex thermal
screening/TSu); Detection limit: 0.02.degree. C./min;
Step: 5 to 20.degree. C.;
[0259] Maximum search temperature: 270.degree. C.; Maximum track
temperature: 300.degree. C.; Maximum pressure: 80 bara.
[0260] The organic nitrates tetradecyl nitrate (TDN), menthyl
nitrate (MN)-- both of the invention, 2-Ethylhexylnitrate (2-EHN;
Aldrich), and di-tert-butylperoxide (DTBP; Merck)--known in the
prior art were assessed in consecutive experiments. Cetane
enhancers were diluted to approx. 15% w/w in toluene for thermal
measurements. Tetradecyl nitrate was also blended at approx. 27%
w/w for PhiTec measurements due to its high molecular weight.
Experiments with DTBP were conducted in an inert atmosphere (under
N.sub.2), which is expected to increase the onset temperature
compared to an oxygen-containing atmosphere. Other experiments were
carried out under air to mimic typical conditions in use. The data
obtained from Phi-Tec measurements are summarised in Table 3.
[0261] The actual start temperature at which the Phi-Tec switched
to adiabatic tracking mode (i.e. first detection of decomposition
onset temperature, DOT) is the temperature of the sample at which
the self-heating rate exceeds 0.02.degree. C./min. From the final
tracking temperature, the adiabatic temperature rise can be
calculated by multiplication with Phi, the heat distribution factor
for the reaction (as is known by the skilled person in the art).
The variable heat capacity (Cp) for the novel nitrates is assumed
to be 2.54 J/gK.
[0262] As indicated in Table 3, in these experiments MN was found
to be slightly less stable than 2-EHN, which correlates with its
effectiveness as a cetane enhancer described above. Overall, TDN
was found to be the most stable molecule, such that the stability
of the compounds was in the order
DTBP<<MN<EHN<<TDN.
[0263] Since the maximum temperature rise is within the Phi-Tec
operating window (i.e. below 400.degree. C.), 1.sup.St order
kinetic data can be obtained from the exothermic decomposition
reaction by plotting in an Arrhenius plot
ln((dT/dt)/60)/(T-T.sub.max)) against 1/T. The frequency factor k
(intercept) and activation energy Ea (slope) can thus be derived.
It is reasonable to assume the decomposition reaction as 1.sup.st
order, as it is solely dependent on the concentration of the
nitrate or peroxide respectively, which approach has been
documented by other investigators (Oxley et al. (2000) Energy &
Fuels, 14, 1252).
TABLE-US-00003 TABLE 3 Kinetic and thermodynamic data derived from
Phi-Tec HWS experiments Phi-tec Conc. Ea Onset Compound (w %)
Atmos. Phi (kJ/mol) Temp. (.degree. C.) DTBP 15.0 N.sub.2 1.10
160.2 111 DTBP 14.6 N.sub.2 1.10 162.0 110 DTBP 14.9 N.sub.2 1.10
157.6 110 DTBP 14.9 N.sub.2 1.10 158.4 112 2-EHN 15.2 air 1.10
178.2 132 2-EHN 14.9 air 1.10 177.5 135 TDN 15.1 air 1.10 190.3 142
TDN 27.2 air 1.10 179.1 136 TDN 27.3 air 1.11 179.5 137 MN 14.9 air
1.10 171.1 123 MN 14.9 air 1.10 171.1 127
[0264] As illustrated in the data, the ranking described for
thermal stability of the compounds is also reflected in the
activation energies (Ea), which indicates that compounds with lower
reaction onset temperature also exhibit lower activation energy.
The reaction enthalpies (not shown) for the respective compounds
correlate with the adiabatic temperature rise. DTBP demonstrated
the lowest reaction enthalpy and the lowest temperature rise,
whereas the organic nitrates compared well, with both the reaction
enthalpy and the adiabatic temperature rise are in the same order
of magnitude.
CONCLUSIONS
[0265] The synthesis of possible alternative embodiments of cetane
enhancers to the commonly used 2-ethylhexylnitrate (2-EHN) was
investigated, with the focus on the use of renewable feedstocks.
There are some safety concerns surrounding the production,
transport and use of this current compound. Furthermore, 2-EHN
functions most effectively under mild engine conditions and a
cetane enhancer that also works well under harsher engine
conditions is desirable.
[0266] Potential cetane enhancers were prepared via the nitration
of various bio-feedstocks: terpene alcohols--borneol, fenchol and
menthol (and pinene); fatty alcohols; unsaturated FAME's;
1,10-Decandiol, ultimately derived from ricinoleic acid (castor
oil); and ethyl abietate, a resin ester derived from tall oil.
[0267] Following determination of the optimum experimental
conditions for nitration in small-scale experiments, different
nitrated products were prepared in 25-50 g scale. The majority of
the samples were well-defined nitrates (R--ONO.sub.2), prepared
from alcohol precursor by reaction with nitric acid, optionally in
combination with other reagents. Treatment of the two olefin
feedstocks with dinitrogen tetroxide (N.sub.2O.sub.4) led to
mixtures of compounds. All samples were characterised by NMR and IR
spectroscopy. DSC/TGA analyses was used to provide information on
the exothermic decomposition of the products. As expected, most
nitrates underwent exothermic decomposition in a narrow temperature
range, around 210.degree. C., whereas products derived from olefins
decomposed over a much broader temperature range.
[0268] Following confirmation (from DSC/TGA and NMR monitoring of
storage stability) that the samples were sufficiently stable to
transport, products were shipped for evaluation of their
effectiveness as cetane enhancers in fuel compositions at a
Combustion Research Unit.
[0269] A thermal screening and calorimetric assessment of the
organic nitrates for use as cetane enhancers has been conducted for
comparison with cetane enhancers known in the art (e.g. 2-EHN and
DTBP).
[0270] Further modifications and alternative embodiments of various
aspects of the invention will be apparent to those skilled in the
art in view of this description. Accordingly, this description is
to be construed as illustrative only and is for the purpose of
teaching those skilled in the art the general manner of carrying
out the invention. It is to be understood that the forms of the
invention shown and described herein are to be taken as the
presently preferred embodiments. Elements and materials may be
substituted for those illustrated and described herein, parts and
processes may be reversed, and certain features of the invention
may be utilized independently, all as would be apparent to one
skilled in the art after having the benefit of this description of
the invention. Changes may be made in the elements described herein
without departing from the spirit and scope of the invention as
described in the following claims.
* * * * *