U.S. patent application number 11/076178 was filed with the patent office on 2005-09-29 for blends of synthetic distillate and biodiesel for low nitrogen oxide emissions from diesel engines.
This patent application is currently assigned to ConocoPhillips Company. Invention is credited to Boehman, Andre L., Esen, Etop, Morris, David P..
Application Number | 20050210739 11/076178 |
Document ID | / |
Family ID | 34975576 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050210739 |
Kind Code |
A1 |
Esen, Etop ; et al. |
September 29, 2005 |
Blends of synthetic distillate and biodiesel for low nitrogen oxide
emissions from diesel engines
Abstract
This invention shows how to make and use a biodiesel-based fuel
in diesel engines without incurring the NO.sub.x penalty.
Embodiments primarily relate to an optimum range of bulk modulus of
compressibility for biodiesel blends, which results in generating
"NO.sub.x neutral" biodiesel blends or to formulate biodiesel
blends with lower NOx emissions than conventional petroleum diesel
fuel. These biodiesel blends preferably comprise synthetic
paraffinic middle distillate derived from a hydrocarbon synthesis
to generate synthetic environmentally-friendly diesel fuels.
Inventors: |
Esen, Etop; (Cypress,
TX) ; Boehman, Andre L.; (State College, PA) ;
Morris, David P.; (McMurray, PA) |
Correspondence
Address: |
DAVID W. WESTPHAL
CONOCOPHILLIPS COMPANY - I.P. Legal
P.O. BOX 1267
PONONCA CITY
OK
74602-1267
US
|
Assignee: |
ConocoPhillips Company
Houston
TX
77079
The Penn State Research Foundation
University Park
PA
16802-7000
|
Family ID: |
34975576 |
Appl. No.: |
11/076178 |
Filed: |
March 9, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60551574 |
Mar 9, 2004 |
|
|
|
Current U.S.
Class: |
44/605 |
Current CPC
Class: |
C10L 1/19 20130101; C10L
1/191 20130101; Y02E 50/10 20130101; C10L 10/02 20130101; C10L 1/18
20130101; C10L 1/026 20130101; C10L 1/14 20130101; C10L 1/1802
20130101; C10L 1/1826 20130101; C10L 1/1616 20130101; Y02E 50/13
20130101 |
Class at
Publication: |
044/605 |
International
Class: |
C10L 001/18 |
Goverment Interests
[0002] This invention was made with United States Government
support under Cooperative Agreement DE-FC26-01NT41098 awarded by
the U.S. Department of Energy and entitled "Development &
Evaluation of New Processes for the Production of Ultra Clean Fuels
from Natural Gas". The United States Government has certain rights
in the invention.
Claims
What is claimed is:
1. A synthetic diesel fuel or diesel fuel blendstock characterized
by producing low sulfur and NOx emissions when used in compression
ignition engines, the synthetic diesel fuel comprising a mixture of
a synthetic middle distillate and a liquid biofuel, said mixture
being characterized by: a sulfur level less than 20 ppm sulfur; a
specific gravity equal to or less than 0.84; a bulk modulus of
compressibility measured at 15 MPa and 37.degree. C. between about
1300 MPa and about 1600 MPa; and a cetane number greater than
55.
2. The synthetic diesel according to claim 1 wherein the synthetic
middle distillate is characterized by a sulfur content less than 10
ppm sulfur and by a specific gravity less than about 0.8.
3. The synthetic diesel according to claim 1 wherein the synthetic
middle distillate is characterized by a cetane number greater than
70.
4. The synthetic diesel according to claim 2 wherein the synthetic
middle distillate is characterized by a cetane number greater than
75.
5. The synthetic diesel according to claim 1 wherein the synthetic
middle distillate is characterized by a paraffin content greater
than 90 percent by weight.
6. The synthetic diesel according to claim 1 wherein the synthetic
middle distillate is characterized by a Bromine number of less than
0.1 gBr/100 g.
7. The synthetic diesel according to claim 1 wherein the synthetic
middle distillate is characterized by an aromatics content of less
than about 1 percent by weight.
8. The synthetic diesel according to claim 1 wherein the synthetic
middle distillate is characterized by a boiling range having a 5%
boiling point between about 170.degree. C. and about 210.degree. C.
and a 95% boiling point between about 320.degree. C. and about
350.degree. C.
9. The synthetic diesel according to claim 1 wherein the liquid
biofuel has a sulfur content less than 30 ppm sulfur.
10. The synthetic diesel according to claim 1 wherein the liquid
biofuel comprises a compound selected from the group consisting of
vegetable oils, alkyl esters of vegetable oils, mixtures of alkyl
esters of fatty acids, and combinations thereof.
11. The synthetic diesel according to claim 1 wherein the liquid
biofuel comprises a mixture of alkyl esters of fatty acids.
12. The synthetic diesel according to claim 1 wherein the liquid
biofuel comprises an alkyl ester of a vegetable oil selected from
the group consisting of canola oil, soybean oil, cotton oil, palm
oil, sunflower oil, and combinations thereof.
13. The synthetic diesel according to claim 1 wherein the liquid
biofuel comprises an alkyl ester of a vegetable oil selected from
the group consisting of canola oil, soybean oil, and combinations
thereof.
14. The synthetic diesel according to claim 1 wherein the amount of
liquid biofuel comprises between about 1 percent by volume and 45
percent by volume of the diesel fuel.
15. The synthetic diesel according to claim 1 wherein the amount of
liquid biofuel comprises between about 1 percent by volume and 20
percent by volume of the diesel fuel.
16. The synthetic diesel according to claim 1 wherein the amount of
liquid biofuel comprises between about 20 percent by volume and 45
percent by volume of the diesel fuel.
17. The synthetic diesel according to claim 1 wherein the synthetic
middle distillate is derived from synthesis gas.
18. The synthetic diesel according to claim 1 wherein the liquid
biofuel comprises a total glycerin content less than 0.24 percent
by weight of glycerin.
19. The synthetic diesel according to claim 1 wherein the liquid
biofuel has a flash point greater than 100.degree. C.
20. The synthetic diesel according to claim 1 wherein the liquid
biofuel has an alcohol content less than 10 percent by weight.
21. The synthetic diesel according to claim 1 wherein the liquid
biofuel has a kinematic viscosity at 40.degree. C. between about
1.9 mm.sup.2/s and about 6 mm.sup.2/s.
22. The synthetic diesel according to claim 1 wherein the synthetic
diesel has a cetane number greater than about 60.
23. The synthetic diesel according to claim 1 wherein the mixture
of the synthetic middle distillate and the liquid biofuel comprises
more than 90 vol. % of the synthetic diesel.
24. A synthetic environmentally-friendly diesel fuel that produces
reduced sulfur and NO.sub.x emissions when used in compression
ignition engines, comprising: a synthetic liquid distillate
characterized by a cetane number greater than 70, by a sulfur
content less than 10 ppm sulfur; by a paraffin content greater than
90 percent by weight; and by a specific gravity less than about
0.8; and a liquid biofuel characterized by a sulfur content less
than 30 ppm sulfur and a specific gravity greater than about 0.86,
wherein the liquid biofuel is derived from a compound selected from
the group consisting of vegetable oils, animal greases, vegetable
oil wastes, microalgae oils, and combinations thereof; wherein the
liquid biofuel is blended with said synthetic liquid fuel so as to
form a synthetic diesel fuel, and wherein the synthetic diesel fuel
has a bulk modulus of compressibility measured at 15 MPa and
37.8.degree. C. between about 1300 MPa and about 1600 MPa; a sulfur
content less than 20 ppmS; and a specific gravity below 0.84.
25. The diesel fuel according to claim 24 wherein the liquid
biofuel comprises a compound selected from the group consisting of
vegetable oils, alkyl esters of vegetable oils, mixtures of alkyl
esters of fatty acids, and combinations thereof.
26. The diesel fuel according to claim 24 wherein the liquid
biofuel comprises a mixture of alkyl esters of fatty acids.
27. The diesel fuel according to claim 24 wherein the liquid
biofuel comprises an alkyl ester of a vegetable oil selected from
the group consisting of canola oil, soybean oil, cotton oil, palm
oil, sunflower oil, and combinations thereof.
28. The diesel fuel according to claim 24 wherein the liquid
biofuel comprises an alkyl ester of a vegetable oil selected from
the group consisting of canola oil, soybean oil, and combinations
thereof.
29. The diesel fuel according to claim 24 wherein the synthetic
diesel fuel comprises between about 1 percent by volume and 45
percent by volume of the liquid biofuel.
30. The diesel fuel fuel according to claim 24 wherein the
synthetic diesel fuel comprises between about 1 percent by volume
and 20 percent by volume of the liquid biofuel.
31. The diesel fuel according to claim 24 wherein the synthetic
diesel fuel comprises between about 20 percent by volume and 45
percent by volume of the liquid biofuel.
32. The diesel fuel according to claim 24 wherein the synthetic
liquid distillate is derived from synthesis gas.
33. The diesel fuel according to claim 24 wherein the synthetic
liquid distillate is characterized by a boiling range having a 5%
boiling point between about 170.degree. C. and about 210.degree. C.
and a 95% boiling point between about 320.degree. C. and about
350.degree. C.
34. The diesel fuel according to claim 24 wherein the liquid
biofuel comprises a total glycerin content less than 0.24 percent
by weight of glycerin.
35. The diesel fuel according to claim 24 wherein the liquid
biofuel has a flash point greater than 100.degree. C.
36. The diesel fuel according to claim 24 wherein the liquid
biofuel has an alcohol content less than 10 percent by weight.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This non-provisional application claims the benefit of U.S.
Provisional Application No. 60/551,574, filed Mar. 9, 2004, which
is hereby incorporated by reference in its entirety
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to the blending of synthetic
products derived from synthesis gas and biomass for the production
of environmentally-friendly diesel fuels, which generate very low
levels of NOx emissions when used in compression ignition
engines.
[0005] 2. Background of the Invention
[0006] A number of performance specifications have been established
for diesel fuels of different grades depending upon service
application. A number of different properties are set out in these
specifications including, for example, flash point, cloud point,
pour point, viscosity, sulfur content, distillation range, gravity
and ignition quality. Of these, the ignition quality is an
important parameter and is usually expressed as cetane number (CN)
determined by the standard ASTM test method D-613. Diesel fuel
properties given the most attention are cetane number, aromatics
content, and sulfur content.
[0007] Internal combustion engines produce emissions containing
water vapor, carbon dioxide, carbon monoxide, unburned
hydrocarbons, oxides of nitrogen (NOx), carbonaceous soot and other
particulate matter. Federal and state regulations dictate the
amount of these and other pollutants, which may be emitted. Oxides
of nitrogen, products of incomplete combustion, and particulates
are considered atmospheric pollutants.
[0008] Sulfur is, of course, associated with the production of
acidic oxides of sulfur, an atmospheric pollutant. These compounds
have been reported to contribute to "acid rain." During combustion
of fuels that contain sulfur compounds, oxides of sulfur
(SO.sub.x), such as sulfur dioxide (SO.sub.2), and sulfur trioxide
(SO.sub.3) are produced as a result of oxidation of the sulfur.
[0009] Some fuels may contain nitrogen compounds that may
contribute to the formation of oxides of nitrogen (NO.sub.x).
NO.sub.x are primarily formed at high temperatures by the reaction
of nitrogen and oxygen from the air used for the reaction with the
fuel.
[0010] Aromatics in diesel fuels are also considered undesirable,
not only for their adverse effect on ignition quality, but also
because they have been implicated in the production of significant
amounts of particulates in the engine exhaust.
[0011] Current environmental regulations are setting stricter
specifications on diesel fuels, especially to address sulfur,
nitrogen, and particulate emissions. Federal and state legislative
bodies and agencies have issued a number of rules applicable to the
production of clean diesel fuel in attempts to reduce emissions.
Many technologies have been developed for reduction of SO.sub.x and
NO.sub.x, but few can remove both types of pollutants
simultaneously in a dry process or reliably achieve cost effective
levels of reduction.
[0012] A rapid series of diesel fuel improvements has been
introduced in most parts of the developed world to provide
reductions in particulates and NOx from the vehicle fleets in
current operation as well as to facilitate the introduction of
after-treatment devices. Reducing the sulfur content and the "heavy
end" of the fuel have been the key changes. Reducing the sulfur
content typically involves the reduction of fuel sulfur via
hydrotreating to levels as low as 10 parts-per-million (or ppm) as
for example, in Swedish Mk 1 fuel. Other fuel parameters such as
aromatics and cetane have also been the subject of
investigation.
[0013] Because of increasingly stringent federal and state
regulations, demand for clean diesel fuels for compression ignition
engines that contain virtually no sulfur and nitrogen, and with
lower aromatic content, will likely increase. Clean diesel fuels
having relatively high cetane number are particularly valuable.
[0014] Clean distillates can be produced from petroleum-based
distillates through severe hydrotreating at great expense. Such
severe hydrotreating imparts relatively little improvement in
cetane number and also adversely impacts the fuel's lubricity as
discussed in an article by Booth & Wolveridge in Oil & Gas
Journal, Aug. 16, 2003, p 71-16. Fuel lubricity, required for the
efficient operation of fuel delivery system, can be improved by the
use of costly additive packages. Specially manufactured fuels and
the incorporation of special fuel components such as biodiesels and
Fisher Tropsch diesels, have been gaining attention.
[0015] The production of clean, high cetane number distillates from
Fischer-Tropsch synthesis has been discussed in the open
literature. Generally, Fischer-Tropsch synthesis converts a mixture
of hydrogen and carbon monoxide (called syngas) to a multitude of
hydrocarbon molecules from 1 to 100 or more carbon atoms. Sources
of synthesis gas can be obtained from reaction of methane or
natural gas with an oxidant (water and/or molecular oxygen) and/or
from gasification of coal, petroleum coke or biomass. The mixture
of hydrocarbons from Fischer-Tropsch synthesis can be distilled,
and its fractions submitted to various hydroprocessing schemes to
generate valuable products such as gasoline, diesel, wax, and/or
lubricants. Since the Fischer-Tropsch synthesis tends to produce
primarily linear hydrocarbons (i.e., normal paraffins), the
Fischer-Tropsch derived diesel product (FT diesel) is of
particularly good quality. Fischer-Tropsch derived diesels
typically have high cetane number (greater than 70), and have very
low sulfur, nitrogen and aromatic contents. Research from Clark and
coworkers disclosed in a 1999 article in Society of Automotive
Engineers (SAE, Warrendale, Pa.) Technical Paper No. 1999-01-2251,
and other studies have shown that FT diesel fuels yield lower
NO.sub.x emissions. Even though the low aromatic content of FT
diesel yields good thermal stability and reduced tendency to form
deposits in engine; the absence of aromatics can result however in
swelling of elastomers in vehicle fuel systems, and hence seal
leakage problems may arise. Moreover, the disclosed hydroprocessing
schemes for preparing Fischer-Tropsch derived distillates also
leave the diesel lacking in one specific property, e.g., lubricity.
The Fischer-Tropsch derived distillates would require blending with
other less desirable stocks or the use of costly additives, such as
a lubricity-enhancing additive.
[0016] Renewable diesel fuels are fuels that are used in diesel
engines in place of or blended with petroleum diesel, but are made
from renewable resources such as vegetable oils, animal fats, or
other types of biomass, such as grasses and trees. Today
Fischer-Tropsch diesel is made from fossil fuels (coal and natural
gas), but a "biosyngas", a synthesis gas generated from biomass,
could be used to make clean liquid fuels in the future.
[0017] Biodiesel is an example of a renewable diesel fuel that is
used across the world today. Biodiesel can be manufactured from
vegetable oils, animal fats, waste vegetable oils (such as recycled
restaurant greases, called yellow grease), microalgae oils, or any
combination thereof, which are all renewable. These feedstocks can
be transformed into biodiesel using a variety of esterification or
transesterification technologies.
[0018] Biodiesel use is growing rapidly, increasing from about 7
million gallons in 2000 to more than 20 million gallons in 2001,
with additional production capacity available to quickly
accommodate further growth. Current U.S. biodiesel production is
based largely on soybean oil and used cooking grease, both of which
are abundant feedstocks. The most frequently used biodiesel
feedstock in Europe is rapeseed (canola) oil. No matter what the
process or the feedstock used, the produced biodiesel must meet
rigorous specifications to be used as a fuel. Fuel-grade biodiesel
must be produced to strict industry specifications, as is described
in the American Society for Testing and Materials method, ASTM
D-6751, in order to insure proper performance in diesel engines.
Technically, biodiesel is defined as a fuel comprised of mono-alkyl
esters of long chain fatty acids derived from vegetable oils or
animal fats, designated B100, and meeting the requirements of ASTM
method D-6751. Fatty-acid alkyl esters are actually long chains of
carbon molecules (8 to 22 carbons long) with an alcohol molecule
attached to one end of the chain. Biodiesel refers to the pure fuel
without blending with a diesel fuel derived from fossil fuels. The
biomass-derived ethyl or methyl esters can be blended with
conventional diesel fuel or used as a neat fuel (100% biodiesel).
Biodiesel blends are denoted as "BXX" with "XX" representing the
percentage of biodiesel contained in the blend (i.e.: B20 is 20%
biodiesel, 80% petroleum diesel; B100 is pure biodiesel). Pure
biodiesel typically requires special treatment in cold weather, due
to a high pour point. Biodiesel, as defined in ASTM D-6751, is
registered with the U.S. Environmental Protection Agency (EPA) as a
fuel and a fuel additive under Section 211(b) of the Clean Air Act.
Biodiesel is used, mostly as a 20% blend (B20) with petroleum
diesel, in federal, state, and transit fleets, private truck
companies, ferries, tourist boats, and launches, locomotives, power
generators, home heating furnaces, and other equipment.
[0019] Biodiesel is non-toxic and biodegradable. It is safe to
handle, transport, and store, and has a higher flash point than
petroleum diesel. Biodiesel can be stored in diesel tanks and
pumped with regular equipment except in colder weather, where tank
heaters or agitators may be required. Biodiesel mixes readily with
petroleum diesel at any blend level, making it a very flexible fuel
additive.
[0020] One of the unique benefits of biodiesel is that it
significantly reduces air pollutants that are associated with
petroleum diesel exhaust. It can help reduce greenhouse gas
emissions, as well as sulfur emissions since biodiesel contains
only trace amounts of sulfur, typically less than the new U.S. EPA
rule finalized in 2001 that will require that sulfur levels in
diesel fuel be reduced from 500 ppm to 15 ppm, a 97% reduction, by
2006.
[0021] However, NO.sub.x emissions are an exception, since in the
case of biodiesel fueling there is a well documented increase of
2-4% in NOx emissions with a blend of 20 vol. % methyl soyate in
petroleum diesel fuel such as is described by Graboski and
McCormick in an article in Progress in Energy and Combustion
Science (1998) vol. 24(2), pp. 125-164, hereafter referred to as
the `Graboski paper`.
[0022] Researchers have been looking for the underlying causes of
the biodiesel "NOx effect". Heywood has shown in "Internal
Combustion Engine Fundamentals", 1988, McGraw-Hill, New York, p.
864, that advancing injection timing can lead to an increase in NOx
emissions from diesel engines. Several researchers have reported an
advance in the fuel injection timing when biodiesel is being used,
such as is described by Choi and coworkers in a 1997 SAE Technical
Paper No. 970218 hereafter referred to as the `Choi paper`, and by
Monyem and coworkers in an article in Transactions of the ASAE
(2001) vol. 44(1), pp. 35-42 hereafter referred to as the `Monyem
paper`. It was further demonstrated by the `Monyem paper` that
there was a linear dependence on NOx and the actual start of
injection, regardless of the fuel used. Szybist and Boehman
described in their 2003 SAE Technical Paper No. 2003-01-1039, which
is incorporated herein by reference in its entirity, the use of a
combination of spray visualization, laser attenuation, fuel line
pressure sensing and heat release analysis to study the impact of
biodiesel blending on the start of injection, end of injection and
ignition delay in an air-cooled single cylinder direct injection
diesel engine. They made comparisons of injection timing and
duration for diesel fuel and a range of biodiesel blends (B20 to
B100). Shifts in injection timing were observed between the fuel
blends, amounting to a 1 crank angle (CA) degree difference between
diesel fuel and pure biodiesel (B100). Combustion studies were also
performed to see how the shift in injection timing affected the
timing of the combustion process. There was an advance in ignition
of up to 4 CA degrees with B100, which can be attributed, at least
in part, to the advanced injection timing.
[0023] Some researchers suggested that differences in the physical
properties of the biodiesel, such as its increased kinematic
viscosity as described in the `Choi paper` or a higher bulk modulus
of compressibility as described in the `Monyem paper`, could lead
to variations in fuel injection timing. Biodiesel has indeed a
higher viscosity (ca. 4.1 mm.sup.2/s at 40.degree. C.) compared to
diesel (ca. 2.6mm.sup.2/s at 40.degree. C.). Viscosity directly
influences the amount of fuel that leaks past the plunger in the
fuel pump and the needle in the fuel injection nozzle. High
viscosity fuels, such as biodiesel, lead to reduced fuel losses
during the injection process compared to lower viscosity fuels,
leading to a faster evolution of pressure, and thus an advance in
fuel injection timing as shown by Tat and Van Gerpen (2003) in
their NREL report NREL/SR-510-31462, p. 114, hereafter referred to
as the `Tat 2003 paper`. Tat and coworkers have previously
suggested in an article in Journal of the American Oil Chemists
Society (2000) vol. 77(3), pp. 285-289, hereafter referred to as
the `Tat 2000 paper`, that a difference in the bulk modulus of
compressibility could be responsible for the difference in fuel
injection timing; and that the NOx increase with biodiesel fueling
is attributable to an inadvertent advance of fuel injection timing.
The effect of viscosity on fuel injection timing relative to the
effect of bulk modulus is currently unknown.
[0024] A diesel fuel injection system was modeled by Rakopoulos and
Hountalas and described in their article in Energy Conversion and
Management, 1996, vol. 37(2), pp. 135-150. The system was separated
into five control volumes. A constant pressure throughout four of
the control volumes could be assumed at any given time: the pumping
chamber, delivery valve chamber, the injector main volume, and the
sac volume. For these volumes the only fuel property that was
important in modeling the pressure as a function of time was the
bulk modulus of compressibility. A less compressible fuel will
result in a faster rise in pressure in the chamber. Constant
pressure throughout the fifth control volume, the fuel line from
the pump to the injector, could not be assumed. The only fuel
properties that were important in modeling the pressure as a
function of time in the fuel line were the density and speed of
sound, which is dependent on the bulk modulus of compressibility.
It was not necessary to take fuel viscosity into account to in
order to validate the model.
[0025] In a similar model of the fuel injection system, a
sensitivity analysis on the effect that the bulk modulus had on the
fuel injection timing was performed by Arcoumanis and coworkers and
described in their 1997 SAE Technical Paper No. 97034. A 10%
increase in the compressibility of the fuel advanced the fuel
injection timing 0.5 CA degrees. By comparison, they found that a
fuel density difference had a negligible effect on the start of
fuel injection. Fuel viscosity was not found to affect the fuel
injection timing.
[0026] Some researchers have reported that certain compositions in
biodiesel were more prone to the "NO.sub.x effect". Biodiesel fuel
composition depends on the feedstock that is subjected to the
transesterifcation process. McCormick and co-workers observed in a
paper in Environmental Science and Technology (2001) vol. 35, pp.
1742-1747, hereafter referred to as the `McCormick 2001 paper`,
that the unsaturated methyl and ethyl esters of fatty acids,
produced from soybean and linseed oils, yield the highest NO.sub.x
increase in a diesel engine. In contrast, the most highly saturated
methyl and ethyl esters of fatty acids, produced from tallow or by
hydrogenating the ethyl and methyl esters, yield much lower NOx
emissions, in some cases even lower than for diesel fuel. McCormick
and co-workers (2001) stated that the fuel chemistry was at the
root of the fuel properties and the increased NO.sub.x
emissions.
[0027] Efforts to combat the "biodiesel NOx effect" have included
blending of biodiesel with various fuel stocks, selection of
different biodiesel feedstocks, and use of cetane improvers.
McCormick's group showed in a 2002 SAE Technical Paper No.
2002-01-1658 hereafter referred to as the `McCormick 2002 paper`,
that a roughly "NO.sub.x neutral" B20 (soybean oil-derived)
biodiesel fuel could be obtained by blending with the biodiesel
with: a diesel blend consisting of 46% Fischer-Tropsch diesel fuel,
a diesel basestock containing 10% aromatics, 1 vol. % di-tert-butyl
peroxide (DTBP), 0.5 vol. % ethyl-hexyl nitrate, or 500 ppm by
volume of ferrocene. In each blend, it appeared that the reduction
in NOx from the base of B20 blended with conventional diesel fuel
arose from enhancing the cetane number of the fuel, which each of
the above cases should provide.
[0028] Consequently, the problem remains that biodiesel (B100 and
B20) increases NO.sub.x emissions from diesel engines. There is
still a need for clean alternate fuels for compression ignition
engines in order to reduce NOx emissions. This invention provides a
more efficient and effective method for blending synthetic
distillates and biofuels to meet current NO.sub.x specification for
diesel specification or to formulate biodiesel blends with reduced
NO.sub.x emissions as well as very low sulfur emissions, without
altering other important fuel specifications related to injection
quality (cetane number).
SUMMARY OF THE INVENTION
[0029] These and other needs in the art are addressed in one
embodiment by a method for forming a synthetic environmentally
friendly diesel fuel or diesel fuel blendstock with reduced sulfur
and NO.sub.x emissions when used in compression ignition engines.
This invention relates to the blending of a synthetic middle
distillate derived from synthesis gas and a biodiesel derived from
biomass for the production of environment-friendly diesel fuels,
which generate very low levels of NO.sub.x and sulfur emissions
when used in diesel engines.
[0030] The invention relates to a synthetic
environmentally-friendly fuel for use in compression ignition
engines, wherein the synthetic environmentally-friendly fuel
comprises a mixture of a synthetic liquid distillate and a liquid
biofuel, and wherein the synthetic environmentally-friendly fuel is
characterized by a sulfur level less than 20 ppmS; a specific
gravity equal to or less than 0.84; a bulk modulus of
compressibility between about 1300 megapascals (MPa) and about 1600
MPa measured at 15 MPa and 37.8 degrees C. (.degree. C.), and a
cetane number greater than 55. The environmentally-friendly diesel
fuel preferably has a specific gravity between about 0.78 and about
0.84. In some embodiments, the synthetic environmentally-friendly
fuel comprises primarily the synthetic liquid distillate and the
liquid biofuel, and may further contains minor components, such as
fuel additives. In alternate embodiments, the synthetic
environmentally-friendly fuel comprises essentially a mixture of
the synthetic liquid distillate and the liquid biofuel.
[0031] As used herein, "biofuel" is defined as a liquid energy
source that is derived from agricultural crops or residues or from
forest products or byproducts and can be substituted for liquid or
gaseous fuels derived from petroleum or other fossil carbon
sources. Biodiesel is one type of biofuel.
[0032] In preferred embodiments, the environmentally-friendly fuel
comprises a volume fraction of the liquid biofuel between about 1
percent and about 45 percent. In alternate embodiments, the
environmentally-friendly fuel comprises a liquid biofuel volume
fraction between 1 percent and 20 percent; or between about 20
percent and 45 percent; or at about 45 percent.
[0033] Other embodiments for the environmentally-friendly fuels for
compression ignition engines include blends of a synthetic
distillate with two or more biofuels from different feedstocks;
blends of two or more synthetic distillates with a biofuel from one
feedstock; or any combination thereof.
[0034] The invention further relates to a method for forming a
synthetic environmentally-friendly diesel fuel or diesel fuel
blendstock, said method comprising blending a liquid biofuel with a
synthetic liquid distillate so as to form a fuel for compression
ignition engines, said fuel being characterized by a bulk modulus
of compressibility measured at 15 MPa and 37.8.degree. C. between
about 1300 MPa and about 1600 MPa, a cetane number greater than
about 55, and wherein the environmentally-friendly diesel fuel
comprises less than 20 ppm sulfur. The specific gravity of the
resulting blend is preferably equal to or lower than 0.84. The
method may further include adjusting the volumetric ratio of
synthetic distillate to biofuel in the fuel so as to meet a
specific gravity of the fuel of less than 0.84.
[0035] The synthetic middle distillate preferably is preferably
derived from a Fischer-Tropsch synthesis. The method for forming a
synthetic environmentally-friendly diesel fuel may further include
the following steps: feeding a synthesis gas to a hydrocarbon
synthesis reactor, wherein the synthesis gas is reacted under
conversion promoting conditions to produce a hydrocarbon synthesis
product; optionally, hydroprocessing at least a portion of said the
hydrocarbon synthesis product to a hydroprocessing unit, wherein
the hydrocarbon synthesis product is hydroprocessed; fractionating
the hydrocarbon synthesis product to at least generate a synthetic
middle distillate, wherein the synthetic middle distillate has a
boiling range comprising a 5% boiling point between about
170.degree. C. and about 210.degree. C. and a 95% boiling point
between about 320.degree. C. and about 350.degree. C.
[0036] The synthetic distillate utilized in the
environmentally-friendly fuel is further characterized by a cetane
number greater than 75, by a sulfur content less than 10 ppm
sulfur; by a paraffin content greater than about 90 percent; and by
a specific gravity less than about 0.8.
[0037] The liquid biofuel in the environmentally-friendly fuel is
preferably characterized by a sulfur content less than 30 ppm
sulfur, and by a specific gravity greater than about 0.86. The
liquid biofuel is derived from biomass such as vegetable oils,
animal fats, waste vegetable oils, and/or microalgae oils.
Preferably, the biofuel comprises an organic compound selected from
the group consisting of esters of fatty acids, hydrogenated esters
of fatty acids, pure vegetable oils, and combinations thereof. The
liquid biofuel more preferably comprises primarily alkyl esters of
fatty acids, wherein said fatty acids are characterized by having
between 8 to 22 carbons atoms. The liquid biofuel is preferably
derived by the esterifcation and/or transesterification of one or
more vegetable oils.
[0038] The invention further relates to a method for forming a
"NO.sub.x neutral" fuel formulation comprising a synthetic liquid
distillate and a liquid biofuel by adjusting the ratio of synthetic
liquid distillate to liquid biofuel to achieve a bulk modulus of
compressibility similar to that of a petroleum diesel
formulation.
[0039] Additionally, the invention relates to a method for forming
a synthetic diesel fuel formulation comprising primarily of a
synthetic distillate and a biofuel within a biofuel volumetric
fraction within an optimum range which comprises a bulk modulus of
compressibility in said synthetic diesel fuel formulation lower
than that of a conventional (crude derived) diesel fuel such that
the synthetic diesel fuel formulation generates reduced NO.sub.x
emissions compared to petroleum diesel fuel formulations.
[0040] The foregoing has outlined rather broadly the features and
technical advantages of the present invention in order that the
detailed description of the invention that follows may be better
understood. Additional features and advantages of the invention
will be described hereinafter that form the subject of the claims
of the invention. It should be appreciated by those skilled in the
art that the conception and the specific embodiments disclosed may
be readily utilized as a basis for modifying or designing other
structures for carrying out the same purposes of the present
invention. It should also be realized by those skilled in the art
that such equivalent constructions do not depart from the spirit
and scope of the invention as set forth in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] For a detailed description of the preferred embodiments of
the invention, reference will now be made to the accompanying
drawings.
[0042] FIG. 1 illustrates the measured bulk modulus as a function
of pressure for biodiesel (B100), FT diesel, blends thereof (B20-FT
and B40-FT), 20% biodiesel blend in petroleum diesel fuel (B20), a
ultra-low sulfur diesel (BP-15), a paraffinic solvent
(Norpar.RTM.), and soy oil;
[0043] FIG. 2 illustrates the relation between the bulk modulus of
compressibility at 15 MPa and 37.8.degree. C. (100.degree. F.) of a
diesel blend with biodiesel and FT diesel with respect to the
biodiesel volume fraction in the diesel blend;
[0044] FIG. 3 illustrates the relation between injection timing
(Crank Angle Variation) and bulk modulus of compressibility
measured at 6.89 MPa and 100.degree. F. for biodiesel (B100),
biodiesel blend with baseline diesel (B20), baseline petroleum
diesel (BP-15), biodiesel blend with FT diesel (B20-FT) and a
paraffin solvent (Norpar.RTM.);
[0045] FIG. 4 illustrates the relation between specific gravity and
bulk modulus of compressibility of various fuels measured at 6.89
MPa and 37.8.degree. C. (100.degree. F.);
[0046] FIG. 5 illustrates a high pressure housing for bulk modulus
measurements; and
[0047] FIG. 6 illustrates the schematic diagram of a spray
visualization chamber connected to a direct injection diesel engine
with access for digital imaging and laser attenuation measurements
of fuel injection timing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0048] To more clearly illustrate the present invention, several
drawings are presented. However, no limitations to the current
invention should be ascertained from the drawings presented herein
below.
[0049] This invention shows how to use a biodiesel-based fuel in
diesel engines without incurring the NO.sub.x penalty, that should
ultimately assist in deploying the use of biodiesels in areas where
ozone non-containment is a problem and a hindrance to biodiesel
utilization.
[0050] Even though there exist physical as well as chemical reasons
for the changes in NO.sub.x emissions with fuels, the Applicants
believe that trends in NO.sub.x emissions can be related primarily
to the bulk modulus of compressibility of the fuel. There exists
therefore an optimum range of bulk modulus of compressibility for
biodiesel blends, which results in generating "NO.sub.x neutral"
biodiesel blends or to formulate biodiesel blends with lower
NO.sub.x emissions than conventional diesel fuel.
[0051] A related factor to the compressibility of the fuel is the
speed of sound. The speed of sound of a fuel can affect the
performance of some types of fuel injection systems, reducing the
time for the pressure pulses to travel from the injection pump to
the injector. All injection systems compress more fuel that is
injected. The bulk modulus and speed of sound of fuels are related
to each other and to fuel density through mathematical
relationships. By measuring a fuel's speed of sound and density,
the adiabatic bulk modulus can be calculated. A higher bulk modulus
of compressibility, or speed of sound, in the fuel blend, leads to
a more rapid transferal of the pressure wave from the fuel pump to
the injector needle and an earlier needle lift. This property, the
bulk modulus of compressibility, can then be associated with fuel
injection performance on biodiesel and blends.
[0052] Tat and coworkers measured and disclosed the bulk modulus of
compressibility for biodiesel and petroleum diesel in the `Tat 2000
paper` from atmospheric pressure to 35 MPa, and showed that the
bulk modulus of compressibility increased linearly with pressure.
Additionally, for the pressure range they studied, the bulk modulus
of biodiesel was always 5-10% higher than diesel fuel. One can
therefore conclude that biodiesel is less compressible than
petroleum diesel.
[0053] The accompanying FIG. 1 shows the measured bulk modulus of
compressibility for some fuel samples: a biodiesel fuel (B100;
methyl soyate), a biodiesel blend B20 with a petroleum diesel, an
unrefined soybean oil, a commercially-available normal paraffin
mixture from C.sub.11-C.sub.15 (Norpar.RTM.-13), a Fischer-Tropsch
diesel, two biodiesel blends with FT diesel (B20-FT; B40-FT), and
an ultra-low sulfur baseline diesel fuel (BP-15). Norpar.RTM. is
the trademark for a line of hydrocarbon fluids with very high
normal paraffin content (>95%) and relatively narrow boiling
ranges, commercially available from ExxonMobil corporation. It will
be understood that other such hydrocarbon fluids can be substituted
therefor. The bulk modulus of compressibility for B20, B100 and the
soybean oil are higher than that of the baseline diesel fuel,
consistent with the results reported in the `Tat 2000 paper`. FIG.
1 also shows that the bulk modulus of compressibility for B20 was
slightly above that of the baseline diesel. One should note that
the "B20" fuel from the `Graboski paper` had between 2 and 4%
higher NOx emissions than the diesel fuel. We can conclude that the
increase in NOx emissions observed for B20 by Graboski and
McCormick in the `Graboski paper` was due to an increase in the
bulk modulus of compressibility of the B20 formulation.
[0054] FIG. 1 also shows that the bulk modulus of the B40-FT blend
is slightly below that of the baseline diesel, and that the B20-FT
blend and FT diesel have significantly lower bulk moduli of
compressibility than the baseline diesel. FIG. 1 therefore shows
that FT diesel and blends of FT diesel comprising up to 40%
biodiesel volume fractions are therefore more compressible than
baseline petroleum diesel.
[0055] FIG. 2 represents the bulk modulus of compressibility for
biodiesel blends with FT diesel versus the biodiesel volumetric
fraction of the blends, 0% being pure FT diesel and 100% being pure
B100. FIG. 2 can be utilized to determine what blend ratio would be
equivalent in bulk modulus to the baseline diesel and what blend
ratio would yield a bulk modulus lower than that of the baseline
diesel. A B45-FT blend corresponds to a bulk modulus of
compressibility at 15 MPa of 1580 MPa, equivalent to that of the
baseline diesel. Hence the B45-FT blend would comprise a "NOx
neutral" biodiesel blend. Accordingly, the biodiesel-FT blends with
less than 45% of biodiesel should give a reduced level of NO.sub.x
emissions when used in a diesel engine compared to a petroleum
diesel or a B20 blend with petroleum diesel, or B100 biodiesel.
Thus, one strategy for combating the biodiesel "NO.sub.x effect" is
to use highly paraffinic diesel fuels, such as FT diesel as the
diesel basestock, in such as way that the bulk modulus of
compressibility is within a desirable range to result in NO.sub.x
emissions equating current petroleum diesel fuel or to result in
even lower NO.sub.x emissions in compression ignition engines than
current petroleum diesel fuel.
[0056] The plot in FIG. 2 also indicates that the bulk modulus of
methyl soyate biodiesel blends with FT diesel increases in a linear
fashion with respect to the biodiesel volumetric fraction in the
blend. This linear fit of bulk modulus of biodiesel blends and
biodiesel fractions should be quite helpful in determining the
optimal range of biodiesel/FT diesel ratios, once the bulk modulus
of compressibility is determined for the pure biodiesel and for
pure FT diesel. A correlation can be established to calculate the
biofuel volume fraction needed in a biofuel/synthetic distillate
blend to make the environmentally-friendly diesel fuel with a
desired bulk modulus of compressibility selected within an optimum
range of bulk moduli of compressibility once the measured bulk
moduli of compressibility of the two main components of the blends:
biofuel and synthetic distillate are measured. This correlation is
shown by Equation (1):
x.sub.b=100(B-B.sub.sd)/(B.sub.b-B.sub.sd) (1)
[0057] wherein B represents the desired bulk modulus of
compressibility of the fuel blend at a specific pressure and a
specific temperature; B.sub.sd represents the measured bulk modulus
of compressibility of the synthetic distillate at the same pressure
and temperature settings; B.sub.b represents the measured bulk
modulus of compressibility of the liquid biofuel at the same
pressure and temperature settings; and x.sub.b represents the
calculated biofuel volume fraction in the resulting fuel blend to
achieve the desired bulk modulus B of compressibility of the fuel
blend.
[0058] FIG. 3 indicates that there is an advance of fuel injection
timing (positive CA change) for the diesel-biodiesel (B20) and pure
biodiesel (B100). B100 has the most advance in fuel injection
timing and also has the highest bulk modulus of compressibility as
shown in FIG. 3. The advanced in injection timing confirms the work
described in the `Choi paper` and the `Monyem paper`. The `Choi
paper` reported an advance in fuel injection timing, 0.6 CA degrees
with a 40% volume blend of biodiesel with a petroleum diesel. The
`Monyem paper` reported an advance in fuel injection timing, based
on the fuel line pressure, of 2.3 CA degrees with neat biodiesel,
and 0.25 to 0.75 CA degrees with a 20% volume blend of biodiesel
using a John Deere 4276 DI engine.
[0059] FIG. 3 also shows that the purely paraffinic solvent,
Norpar.RTM., and the 20% blend of B100 and FT diesel (B20-FT)
retard the fuel injection timing by 0.5 CA and 0.1 CA respectively,
compared to the baseline diesel (BP-15). Norpar.RTM. has the most
retardation in fuel injection timing and also has the lowest bulk
modulus of compressibility as shown in FIG. 3. This retardation in
injection timing associated with the paraffinic mixture gives
support to the proposition that variation in injection timing due
to the lower bulk modulus of compressibility is a contributing
factor in the reductions in NO.sub.x emissions observed with FT
diesel fuels. And, the retarded injection timing provides an
explanation for the reduced NO.sub.x emissions measured by
McCormick's group and reported in the `McCormick 2002 paper` when
they blended FT diesel with conventional diesel to produce a partly
paraffinic base for a B20 blend.
[0060] The data in FIGS. 1 and 3 for bulk modulus and injection
timing show that there is a trend on which one can base a judgment
about the potential impact of a fuel on injection timing and
emissions. There is an increase in bulk modulus with increasing
density. FIG. 4 shows the specific gravity of various fuels versus
their respective bulk modulus, and the specific gravity of the
fuels is correlated directly with the bulk modulus. The fuels
represented in FIG. 4 include data from several published sources:
the `McCormick 2001 paper`; the `Tat 2003 paper`, and an article by
Ofner et al. in Inst. Mech. Engr. J. (1996) "A fuel injection
system concept for dimethyl ether," vol. 22, pp. 275-287 hereafter
referred to as the `Ofner paper`. The `Tat 2003 paper` presented a
survey of the bulk moduli of the various methyl and ethyl esters at
6.89 MPa (1000 psi), that are common in biodiesel fuels albeit
measured at a slightly higher temperature of 40.degree. C.
(104.degree. F.). The lowest density in FIG. 4 represents dimethyl
ether with the lowest bulk modulus (B.about.450 MPa at 3.4 MPa
pressure), which originates from the `Ofner paper`. Hence, FIG. 4
shows a definitive trend between bulk modulus and fuel density,
since the bulk modulus generally seems to increase with an increase
in fuel specific gravity. That trend can be represented by a linear
relationship as shown in Equation (2) with a correlation
coefficient R.sup.2=0.925
B=-2,666+4,966*SG (2)
[0061] where B is the bulk modulus of compressibility in MPa and SG
is the specific gravity. Although there seems to be a correlation
between specific gravity and bulk modulus of compressibility for
these fuels, it is to be noted however that fuels of similar
specific gravity can differ by 20 MPa or more, or 50 MPa or more,
or sometimes 100 MPa or more in bulk modulus of compressibility,
and that the bulk modulus of compressibility of a fuel could be
lower than that of a fuel with a lower specific gravity, as
illustrated by the scatter of data points for the various fuels
with specific gravity between about 0.84 and 0.89. Similarly, the
actual bulk modulus for dimethyl ether (with the lowest specific
gravity) is much lower than would have been predicted with Equation
(2).
[0062] The NO.sub.x emissions trends observed in the `McCormick
2001 paper` for the speciated biodiesel constituents and various
biodiesel feedstocks can be explained, in light of the present
work, on the basis of the variation of the bulk modulus of the
fuels, consistent with the observations by Van Gerpen and
co-workers disclosed in the `Monyem paper` and the `Tat 2002
paper.` These same observations have relevance to the formulation
of reformulated diesel fuels, FT diesel fuels, biodiesel fuels
(B20, B100, etc.) and blends thereof.
[0063] These observations on the correlation of bulk modulus with
density are consistent with the historical literature on the bulk
modulus of hydrocarbons. Bridgman in his 1958 book "The Physics of
High Pressure", published by G. Bell and Sons (London), pp. 116-149
described the methodologies for testing the compressibility of
fluids and presented a summary of results that were available at
that time for various fluids, including normal alkanes,
iso-alkanes, alcohols, halogenated compounds and water. Bridgman
asserted that the compressibility of fluids at lower pressures was
due to consumption of free space between the loosely packed
molecules. At higher pressures, the compressibility is less and is
due to compression of the molecules themselves that would be
opposed by intermolecular repulsion. Thus, the bulk modulus should
increase with increasing pressure as the resistance to further
compression increases.
[0064] Similar trends in compressibility of hydrocarbons were
observed by Cutler and coworkers in their paper in the Journal of
Chemical Physics (1958) vol. 29, pp. 727-740 hereafter referred to
as the `Cutler paper`, who considered a variety of pure
hydrocarbons including normal alkanes from C.sub.12 to C.sub.18,
branched alkanes, cycloalkanes and aromatic compounds. The `Cutler
paper` disclosed that compressibility was greatest for normal
alkanes, which have a less rigid structure, and decreased with
increasing rigidity of molecular shape. Thus, compressibility
increased as molecular structure varied from multi-ring aromatic,
to aromatic, to cycloalkane, to branched alkane, and to
straight-chain alkane. Since the bulk modulus is inversely related
to the compressibility, the trend for bulk modulus would be to
increase with increasing rigidity. Following Bridgman's logic, the
bulk modulus would also increase with increasing density, because a
more dense fluid would possess less of the free space to be
consumed during compression.
[0065] For the various biodiesel fuel stocks considered in the
`McCormick 2001 paper`, there appears to be a strong correlation
between NO.sub.x emissions and density. An underlying reason for
the trend of increasing NO.sub.x with increasing density (and
Iodine Number, which is an indication of the degree of
unsaturation) is that as the density of the biodiesel feedstock
increases, its bulk modulus increases and leads to advanced
injection timing.
[0066] The Applicants believe that the higher bulk modulus of
compressibility of vegetable oils and their methyl esters leads to
advanced injection timing. Advanced injection timing has been shown
in the literature to contribute to the NO.sub.x emissions increase
with the use of biodiesel fuel. An opposite trend, a retarding of
injection timing, is observed with paraffinic mixtures because they
have a lower bulk modulus of compressibility than conventional
diesel fuels. This supports the observation that paraffinic fuels
such as Fischer-Tropsch diesel fuels yield lower NO.sub.x
emissions. Thus, the biodiesel "NOx effect" can be attributed to
variations in the bulk modulus of the fuel or fuel blend, and these
effects correlate for biofuels and paraffinic fuels quite well with
fuel density.
[0067] The present work also shows that a 45 vol. % blend of a
methyl soyate biodiesel and a FT diesel displays the same bulk
modulus of compressibility as a ultra-low sulfur petroleum diesel
fuel. Thus, one strategy for combating the biodiesel "NOx effect"
is to use highly paraffinic diesel fuels, such as FT diesel as the
diesel basestock.
[0068] Blends of Biofuel and Synthetic Distillate
[0069] The invention relates to a synthetic
environmentally-friendly fuel or diesel fuel blendstock (generally
referred to collectively herein as a "fuel") for use in compression
ignition engines, the synthetic fuel comprising a mixture of a
synthetic liquid distillate and a liquid biofuel, said mixture
being characterized by a sulfur level less than 20 ppm S; a
specific gravity equal to or less than 0.84; a bulk modulus of
compressibility between about 1300 MPa and about 1600 MPa measured
at 15 MPa and 37.8.degree. C., and a cetane number greater than 55.
The environmentally-friendly diesel fuel preferably has a specific
gravity between about 0.78 and about 0.84. Preferably, the
environmentally-friendly diesel fuel has a cetane number greater
than about 60; more preferably, a cetane number greater than about
65.
[0070] In some embodiments, the synthetic environmentally-friendly
fuel comprises primarily at least one synthetic liquid distillate
and at least one liquid biofuel (i.e., greater than 90% volume
comprises both components), and may further contain minor
components, such as fuel additives.
[0071] In alternate embodiments, the synthetic
environmentally-friendly fuel comprises essentially of a mixture of
at least one synthetic liquid distillate and at least one liquid
biofuel (i.e., greater than 95% volume comprises both
components).
[0072] Since biofuels tend to increase the bulk modulus of
compressibility, and the paraffinic fuels tend to decrease the bulk
modulus of compressibility, there exists an optimum biofuel volume
fraction in the synthetic fuel blends that yields a bulk modulus of
compressibility about equal to that of a petroleum diesel fuel so
as to achieve "NO.sub.x neutral" synthetic fuels. The preferred
biodiesel blends of the present invention comprise a synthetic
middle distillate, such that the NOx effect is mitigated by the
selection of an optimum range of bulk modulus of compressibility
for each biodiesel blend. This optimum range of bulk modulus of
compressibility is primarily dependent on a specific range of
volumetric ratios of synthetic middle distillate to biodiesel in
the biodiesel blend, and the respective bulk modulus of
compressibility of pure synthetic middle distillate and pure
biodiesel.
[0073] The environmentally-friendly fuel preferably comprises a
volume fraction of liquid biofuel between about 1 percent and about
45 percent. In these preferred embodiments, the
environmentally-friendly fuel comprises a bulk modulus of
compressibility measured at 15 MPa and 37.8.degree. C. between
about 1300 MPa and about 1600 MPa, and a cetane number greater than
55.
[0074] In alternate embodiments, the environmentally-friendly fuel
comprises a liquid biofuel volume fraction between 1 percent and 20
percent; or between about 20 percent and 45 percent; or at about 45
percent.
[0075] The environmentally-friendly fuel comprising a volume
percent of liquid biofuel between 1 percent and 20 percent has a
bulk modulus of compressibility measured at 15 MPa and 37.8.degree.
C. between about 1300 MPa and about 1500 MPa, and a cetane number
greater than 70.
[0076] In alternate embodiments, the environmentally-friendly fuel
comprises a volume percent of liquid biofuel between about 20
percent and 45 percent has a bulk modulus of compressibility
measured at 15 MPa and 37.8.degree. C. between about 1500 MPa and
about 1600 MPa; a cetane number greater than about 60; and a
specific gravity between about 0.8 and about 0.84.
[0077] In alternate embodiments, the environmentally-friendly fuel
comprises a volume percent of liquid biofuel of about 45 percent so
that the fuel has a bulk modulus of compressibility measured at 15
MPa and 37.8.degree. C. between about 1560 MPa and about 1600
MPa.
[0078] In additional embodiments, the environmentally-friendly fuel
comprises a biofuel to synthetic distillate volumetric ratio
between 0.01 and about 0.45; or between 0.01 and about 0.2; between
0.2 and about 0.45; or at about 0.45.
[0079] In preferred embodiments, the synthetic distillate is a FT
diesel distillate. FT Diesel distillate can be combined with the
biofuel in any ratio suitable to reduce the bulk modulus of
compressibility of the blend to a desired value so as to produce a
diesel fuel with "NOx neutral" effect which produced reduced NOx
emissions when used in a diesel engine compared to a conventional
petroleum diesel.
[0080] In alternative embodiments, FT diesel distillate can be
combined with biofuel to reduce the density of the resulting blend
for any desired reason. For instance, a biofuel can be combined
with FT diesel distillate to satisfy density specifications for a
diesel fuel. Typically, these specifications determine allowable
uses of diesel fuel, classifications of diesel fuel, and the like,
which are all well known. Examples of allowable uses of a diesel
fuel include on-road use, off-road use, and the like. For instance,
regulations may require that the diesel fuel have a density within
a specified range to qualify as an on-road use diesel fuel. The
regulations may also require the diesel fuel to comprise other
properties, such as cetane number, sulfur content, aromatics
content, and the like, within a specified range to qualify as the
on-road use diesel fuel. An example of classifications for diesel
fuels includes specifications for a No. 2 diesel fuel. These
classifications are well known and include World-Wide Fuel Charter
classifications, ASTM classifications, European classifications,
and the like. For instance, the December 2002 World-Wide Fuel
Charter recommends a density range measured at 15.degree. C. of
about 820 kg/m.sup.3 to about 850 kg/m.sup.3 (the minimum limit can
be relaxed to 800 kg/m.sup.3 when ambient temperatures are below
-30.degree. C.) for a No. 2 diesel fuel. To bring an off-spec
synthetic mixture such as a FT diesel and a biofuel to within the
density specifications of the 2002 World-Wide Fuel Charter
specifications for a No. 2 diesel fuel, FT diesel distillate can be
combined with a biofuel comprising mono-alkyl esters of fatty acids
to form a diesel product in a desired ratio to bring the density of
the diesel product within the specification limits of 815
kg/m.sup.3 to about 850 kg/m.sup.3, as long as the bulk modulus of
compressibility is within or below the "NO.sub.x neutral" zone for
diesel.
[0081] The FT diesel distillate can be further blended with the
biofuel to achieve a specific gravity of the blend below 0.84 and
to adjust at least one other property of the blend, wherein the
other properties include the cetane number, lubricity, iodine
number, viscosity, and the like.
[0082] With the FT diesel distillate preferably having a density at
15.degree. C. from about 0.76 g/cm.sup.3 to about 0.80 g/cm.sup.3,
more preferably between about 0.77 g/cm.sup.3 to about 0.79
g/cm.sup.3, FT diesel distillate can be combined with a biofuel
having a higher bulk modulus of compressibility than FT diesel
distillate to produce a synthetic diesel fuel having a bulk modulus
of compressibility lower than that of the biofuel. The FT diesel
distillate can be combined with biofuel by any known method. In the
present embodiment, the FT diesel distillate is combined with the
biofuel in a vessel.
[0083] Preferably, the environmentally-friendly fuel has a sulfur
level less than 15 ppm S; more preferably less than 10 ppm S; still
more preferably less than 5 ppm S.
[0084] Preferably, the environmentally-friendly fuel for
compression ignition engines has a boiling range with a 5% boiling
point between about 320.degree. F. and 350.degree. F. (about
160-177.degree. C.) and a 95% boiling point between about
600.degree. F. and 650.degree. F. (about 315-343.degree. C.).
[0085] In another embodiment, the environmentally-friendly
synthetic liquid fuel has a boiling range having a 5% boiling point
between about 340.degree. F. and about 410.degree. F. (or between
about 170.degree. C. and about 210.degree. C.) and a 95% boiling
point between about 570.degree. F. and about 645.degree. F. (or
between about 300.degree. C. and about 340.degree. C.).
[0086] Alternatively, the environmentally-friendly synthetic liquid
fuel has a boiling range having a 5% boiling point between about
355.degree. F. and about 420.degree. F. (or between about
180.degree. C. and about 215.degree. C.) and a 95% boiling point
between about 600.degree. F. and 650.degree. F. (or between about
315.degree. C. and 343.degree. C.).
[0087] Biofuel
[0088] The biofuel or blendstock should comprise one or more
organic compounds selected from the group consisting of esters of
fatty acids, hydrogenated esters of fatty acids, pure vegetable
oils, and combinations thereof. The liquid biofuel more preferably
comprises primarily alkyl esters of fatty acids, each having
between 8 to 22 carbon atoms. Preferred esters of fatty acids are
methyl esters, ethyl esters, or combinations thereof, of fatty
acids, said fatty acids comprising between 8 and 22 carbon atoms.
Examples of suitable fatty acid esters are methyl laurate, methyl
palmitate, methyl stearate, ethyl stearate, methyl oleate, methyl
linoleate, ethyl linoleate, methyl linolenate, and the like.
[0089] The biofuel preferably comprises a density higher than about
the density of synthetic distillate. The biofuel preferably
comprises mono-alkyl esters of fatty acids which include products
of esterification and/or transesterification of vegetable oils,
animal fats, and yellow grease, said products comprising very small
amounts of glycerol and/or alcohol. More preferably, the liquid
biofuel comprises an alkyl ester of one or more vegetable oils
selected from the group consisting of canola oil, cotton oil,
sunflower oil, coconut oil, palm oil, soya oil, and combinations
thereof. Still more preferably, the liquid biofuel comprises alkyl
esters of fatty acids produced from soybean oil and/or canola oil,
wherein the alkyl esters are methyl esters, ethyl esters, or
combinations thereof. In some embodiments, the liquid biofuel
comprises methyl soyate.
[0090] The liquid biofuel can be characterized by a bulk modulus of
compressibility measured at 15 MPa and 37.8.degree. C. greater than
about 1600 MPa, preferably between about 1650 MPa and about 2100
MPa.
[0091] Furthermore, the biofuel has a very low sulfur content,
i.e., less than 50 ppm sulfur, preferably less than 30 ppm sulfur,
preferably less than 10 ppm sulfur. Biodiesel comprising canola oil
and/or canola alkyl esters, may have a sulfur content slightly
higher than from other feedstocks. The biofuel should also have
very low aromatic and nitrogen contents.
[0092] In addition, the liquid biofuel is preferably substantially
free of glycerin, i.e., the total glycerin content of the liquid
biofuel should be less than 0.24 percent by weight. The `free`
glycerol content is preferably less than 0.02 percent by weight.
The free and total glycerin can be measured employing the ASTM
method D-6584 "Test Method for Determination of Free and Total
Glycerine in B-100 Biodiesel Methyl Esters by Gas Chromatography".
In some embodiments, the liquid biofuel comprises a substantially
glycerin-free product of the esterification of soya oil, canola oil
or mixtures thereof.
[0093] Preferably, the liquid biofuel has a specific gravity
greater than about 0.86; more preferably between about 0.86 and
about 0.91; still more preferably between about 0.86 and about
0.89.
[0094] The liquid biofuel is not meant to comprise essentially
alcohols, such as methanol and ethanol, which also can be derived
from biomass (renewable resources). The liquid biofuel preferably
should contain a very low content of `free` (i.e., unbound) alcohol
molecules, i.e., less than about 10 percent by weight.
[0095] In the case when the method of making the liquid biofuel
includes the use of an alcohol during the esterification process
described later, the flash point for biodiesel is used as the
mechanism to limit the level of un-reacted alcohol remaining in the
finished fuel. The flash point specification for biodiesel is
intended to be 100.degree. C. minimum. Typical values are over
160.degree. C. Due to high variability with the ASTM Method D-93
"Standard Test Methods for Flash-Point by Pensky-Martens Closed Cup
Tester" as the flash point approaches 100.degree. C., the flash
point specification has been set at 130.degree. C. minimum to
ensure an actual value of 100.degree. C. minimum. The flash point
of the liquid biofuel is preferably greater than 100.degree. C.;
more preferably greater than 130.degree. C.
[0096] The liquid biofuel preferably has a boiling range with an
initial boiling point between about 300.degree. C. and about
330.degree. C. and a final boiling point between about 350.degree.
C. and about 370.degree. C. according to the ASTM distillation
method D-86 "Standard Test Method for Distillation of Petroleum
Products at Atmospheric Pressure"; or a boiling range with an
initial boiling point between about 310.degree. C. and about
350.degree. C. and a final boiling point between about 400.degree.
C. and about 480.degree. C. according to the ASTM vacuum
distillation method D-1160 "Standard Test Method for Distillation
of Petroleum Products at Reduced Pressure".
[0097] The kinematic viscosity at 40.degree. C. of the liquid
biofuel can be between about 1.9 mm.sup.2/s (cSt) and about 6 cSt,
but preferably between 3 cSt and 6 cSt. The kinematic viscosity at
40.degree. C. is preferably measured by the ASTM method D-445
"Standard Test Method for Kinematic Viscosity of Transparent and
Opaque Liquids (the Calculation of Dynamic Viscosity)".
[0098] The cetane number of the liquid biofuel is preferably
greater than 43; more preferably between about 45 and about 65;
still more preferably between about 50 and about 60. The cetane
number is preferably measured by the ASTM method D-613 "Standard
Test Method for Cetane Number of Diesel Fuel Oil".
[0099] The density at 15.degree. C. of the liquid biofuel is
preferably between about 0.86 g/cm.sup.3 and about 0.91 g/cm.sup.3;
more preferably between about 0.87 g/cm.sup.3 and about 0.89
g/cm.sup.3. The density at 15.degree. C. can be measured by the
ASTM method D-4052 "Standard Test Method for Density and Relative
Density of Liquids by Digital Density Meter".
[0100] The specific gravity of the liquid biofuel is preferably
between about 0.86 and about 0.91; more preferably between about
0.87 and about 0.89 as measured by the ASTM method D-1298 "Standard
Test Method for Density, Relative Density (Specific Gravity), or
API Gravity of Crude Petroleum and Liquid Petroleum Products by
Hydrometer Method".
[0101] In preferred embodiments, the liquid biofuel meets the
specifications of the ASTM method D-6751 specifications "Standard
Specification for Biodiesel Fuel (B100) Blend Stock for Distillate
Fuels".
[0102] Methods of Synthesizing Biofuel
[0103] The liquid biofuel is preferably manufactured from vegetable
oils, animal fats, waste vegetable oils (such as recycled
restaurant greases, called yellow grease) and microalgae oils, or
any combination thereof. Methods of preparation of biodiesel are
well known. The feedstocks can be transformed into biodiesel using
a variety of esterification or transesterification technologies.
Oils and fats are composed principally of triglycerides, composed
of three long-chain fatty acids of 8 to 22 carbons attached to a
glycerol backbone, and free fatty acids, which fatty acid chains
break off the triglycerides.
[0104] The biofuel is preferably synthesized by esterification
and/or transesterification of one or more feesdstocks selected from
the groups consisting of vegetable oils (e.g., canola oil, soybean
oil, linseed oil, and the like), animal fats (e.g., beef tallow,
pork lard), waste vegetable oils (e.g., yellow grease), and
microalgae oils.
[0105] Biodiesel feedstocks are classified based on the free fatty
acid (FFA) content: refined oils (such as refined soybean and
canola oils with less than 1.5% FFA), low FFA yellow greases and
animal fats (<4% FFA), and high FFA yellow greases and animal
fats (>20%). The production of biodiesel from low FFA fats and
oils comprises a base catalyzed transesterification, wherein the
triglycerides are transformed into biodiesel and glycerine under
base conditions. The production of biodiesel from high FFA fats and
oils comprises an acid esterification, wherein FFA are reacted with
an alcohol (usually ethanol or methanol) in the presence of an acid
(such as sulfuric acid) to form fatty esters such as ethyl or
methyl esters. The esterification reaction is then followed by a
transesterification.
[0106] The liquid biofuel comprising alkyl esters is preferably
produced by the base catalyzed reaction because it is the most
economic for several reasons: low temperature (65.degree. C. or
150.degree. F.) and pressure (20 psi) processing; high conversion
(98%) with minimal side reactions and reaction time; direct
conversion to methyl ester with no intermediate steps; and no need
for expensive materials of construction. The general process is
depicted as follows: a fat or oil is reacted with an alcohol, like
methanol or ethanol, in the presence of a catalyst to produce
glycerin and alkyl esters (i.e., biofuel). The alcohol is charged
in excess to assist in quick conversion and recovered for reuse.
The catalyst is usually sodium or potassium hydroxide which has
already been mixed with the methanol.
[0107] An overview of present processes from various biodiesel
feedstocks was described by Kinast in his Final Report to
USDOE/National Renewable Energy laboratory, contact ACG-7-15177-02,
September 1999. Additional processes for making biofuel are
described by Canakci and Van Gerpen in their paper from
Transactions of the American Society of Agricultural Engineers
(2001) vol. 44, No. 6, pp. 1429-1436; as well as in their paper
from Transactions of the American Society of Agricultural Engineers
(1999) vol. 42, No. 5, pp. 1203-12; and by Freedman and coworkers
in an article in the Journal of the American Oil Chemists' Society
(1984) vol. 61, p. 1638.
[0108] Synthetic Distillate
[0109] The synthetic liquid distillate preferably has a boiling
range having a 5% boiling point between about 170.degree. C. and
about 210.degree. C. and a 95% boiling point between about
320.degree. C. and about 350.degree. C. These boiling points are
based on the method ASTM D-86 from the American Society for Testing
and Materials.
[0110] The synthetic liquid distillate preferably has a density at
15.degree. C. of from about 0.76 g/cm.sup.3 to about 0.80
g/cm.sup.3; and more preferably between about 0.77 g/cm.sup.3 and
about 0.79 g/cm.sup.3; most preferably at about 0.78
g/cm.sup.3.
[0111] In addition, the synthetic liquid distillate is
characterized by a paraffin content greater than about 90 percent,
preferably greater than about 95 percent. The synthetic liquid
distillate should have a sulfur content of less than about 10 ppm
sulfur; preferably less than about 5 ppm sulfur; more preferably
less than 1 ppm sulfur; still more preferably less than about 0.1
ppm sulfur. Moreover, the synthetic liquid distillate preferably
has an aromatics content of less than about 1 percent by
weight.
[0112] Furthermore, the synthetic liquid distillate preferably has
a cetane number greater than about 70, preferably greater than
about 75. It is to be understood that the synthetic liquid
distillate is not limited to the above-identified property values
but can include higher or lower values depending on factors such as
the synthesis conditions and the hydroprocessing scheme and
conditions used to produce it.
[0113] In some embodiments, the synthetic liquid distillate
comprises very small amounts of olefins, i.e., less than 10 percent
by weight, preferably less than 5 percent by weight. In alternate
embodiments, the synthetic liquid distillate is characterized by a
Bromine number of less than about 0.1 g/100 g as measured by the
ASTM method D-1159 "Standard Test Method for Bromine Numbers of
Petroleum Distillates and Commercial Aliphatic Olefins by
Electrometric Titration".
[0114] Most of the synthetic liquid distillate used in the
environmental-friendly fuel is preferably generated by a
Fischer-Tropsch synthesis described herein.
[0115] Methods of Preparing Synthetic Distillate by Fischer-Tropsch
Process
[0116] A syngas feed is fed to hydrocarbon synthesis reactor.
Syngas comprises hydrogen, or a hydrogen source, and carbon
monoxide. Hydrocarbon synthesis reactor comprises any reactor in
which hydrocarbons are produced from syngas by Fischer-Tropsch
synthesis, alcohol synthesis, and any other suitable synthesis.
Hydrocarbon synthesis reactor is preferably a Fischer-Tropsch
reactor. Preferably, the hydrogen is provided by free hydrogen,
although some Fischer-Tropsch catalysts have sufficient water gas
shift activity to convert some water (and CO) to hydrogen (and
CO.sub.2) for use in the Fischer-Tropsch synthesis. It is preferred
that the molar ratio of hydrogen to carbon monoxide in syngas feed
60 be greater than 0.5:1 (e.g., from about 0.67 to about 2.5).
Preferably, when cobalt, nickel, and/or ruthenium catalysts are
used, syngas feed contains hydrogen and carbon monoxide in a molar
ratio of about 1.4:1 to about 2.3:1. Preferably, when iron
catalysts are used, syngas feed 60 contains hydrogen and carbon
monoxide in a molar ratio between about 1.4:1 and about 2.2:1.
Syngas feed may also contain carbon dioxide. Moreover, syngas feed
should contain only a low concentration of compounds or elements
that have a deleterious effect on the catalyst, such as poisons.
For example, syngas feed may need to be pretreated to ensure that
it contains low concentrations of sulfur or nitrogen compounds such
as hydrogen sulfide, hydrogen cyanide, ammonia and carbonyl
sulfides.
[0117] Syngas feed is contacted with the catalyst in a reaction
zone. Mechanical arrangements of conventional design may be
employed as the reaction zone including, for example, fixed bed,
fluidized bed, slurry bubble column or ebullating bed reactors,
among others. Accordingly, the preferred size and physical form of
the catalyst particles may vary depending on the reactor in which
they are to be used. A slurry bed reactor with catalyst particles
with a weight size average between 30 and 150 microns is preferred.
The catalyst in the reaction zone for hydrocarbon synthesis
preferably comprises a catalytically active metal selected from the
group consisting of cobalt, iron, ruthenium, and combinations
thereof. More preferably, the catalyst in the reaction zone for
hydrocarbon synthesis preferably comprises cobalt as one
catalytically active metal. The catalyst may further comprise at
least one promoter suitable for increasing the selectivity,
stability, and/or activity of the reduced catalyst. Suitable
promoters are preferably selected from the group consisting of
ruthenium, rhenium, platinum, palladium, boron, manganese,
magnesium, silver, lithium, sodium, copper, potassium, and
combination thereof. The reduced catalyst may be supported or
unsupported. The support for a supported catalyst preferably
includes an inorganic oxide such as silica, alumina, titania, or
any combination thereof.
[0118] The Fischer-Tropsch reactor is typically run in a continuous
mode. In this mode, the gas hourly space velocity through the
reaction zone typically may range from about 50 to about 10,000
hr.sup.-1, preferably from about 300 hr.sup.-1 to about 2,000
hr.sup.-1. The gas hourly space velocity is defined as the volume
of reactants per time per reaction zone volume. The volume of
reactant gases is preferably at but not limited to standard
conditions of pressure (101 kPa) and temperature (0.degree. C.).
The reaction zone volume is defined by the portion of the reaction
vessel volume where the reaction takes place and which is occupied
by a gaseous phase comprising reactants, products and/or inerts; a
liquid phase comprising liquid/wax products and/or other liquids;
and a solid phase comprising catalyst. The reaction zone
temperature is typically in the range from about 160.degree. C. to
about 300.degree. C. Preferably, the reaction zone is operated at
conversion promoting conditions at temperatures from about
190.degree. C. to about 260.degree. C.; more preferably, from about
205.degree. C. to about 230.degree. C. The reaction zone pressure
is typically in the range of about 80 psia (552 kPa) to about 1,000
psia (6,895 kPa), more preferably from 80 psia (552 kPa) to about
800 psia (5,515 kPa), and still more preferably, from about 140
psia (965 kPa) to about 750 psia (5,170 kPa). Most preferably, the
reaction zone pressure is from about 250 psia (1,720 kPa) to about
650 psia (4,480 kPa).
[0119] The product of hydrocarbon synthesis reactor primarily
comprises hydrocarbons. Hydrocarbon synthesis product may also
comprise olefins, alcohols, aldehydes, and the like. Hydrocarbon
synthesis product primarily comprises paraffins (more than 80%
paraffins).
[0120] The hydrocarbon synthesis process should also comprise a
fractionator in order for the product of hydrocarbon synthesis
reactor to be separated into various fractions, including a
gasoline fraction and middle distillate fractions (including diesel
fraction). Methods of fractionation are well known in the art, and
the feed to the fractionator can be separated by any suitable
fractionation method. The fractionator preferably includes an
atmospheric distillation column.
[0121] The method for making the synthetic distillate may further
comprise feeding the hydrocarbon synthesis product to a
hydroprocessing unit, wherein the hydrocarbon synthesis product is
hydroprocessed to produce a hydroprocessed product; fractionating
the hydroprocessed product to produce a treated distillate; and
combining the treated distillate with a liquid biofuel to produce a
fuel, wherein the fuel has a bulk modulus within an optimum range
and a cetane number greater than 55.
[0122] Hydrocarbon synthesis product in part or in totality is
preferably further hydroprocessed in order to generate an
acceptable yield of liquid fuels such as gasoline and diesel.
Hydroprocessing could be done on the totality or a portion of the
hydrocarbon synthesis product. Hydroprocessing could comprise
hydrotreatment, hydrocracking, hydroisomerization, dewaxing, or any
combination thereof.
[0123] In some embodiments, the hydroprocessing comprises a
hydrotreatment to reduce the olefin content of the distillate so
that the Bromine number (related to unsaturation of carbon-carbon
bonds) is less than 0.1 g/100 g as measured for example by ASTM
method D-1159 "Standard Test Method for Bromine Numbers of
Petroleum Distillates and Commercial Aliphatic Olefins by
Electrometric Titration".
[0124] The hydrotreatment should convert unsaturated hydrocarbons
(such as olefins) to saturated hydrocarbons (such as alkanes). The
hydrotreatment can take place over hydrotreating catalysts. The
hydrotreating catalysts comprise at least one of a group VIB metal,
such as molybdenum and tungsten, or a group VIII metal, such as
nickel, palladium, platinum, ruthenium, iron, and cobalt. The
nickel, palladium, platinum, tungsten, molybdenum, ruthenium, and
combinations thereof are typically highly active catalysts, and the
iron and cobalt are typically less active catalysts. The
hydrotreatment is preferably conducted at temperatures from about
140.degree. C. to about 315.degree. C. Other operating parameters
of hydrotreatment may be varied by one of ordinary skill in the art
to affect the desired hydrotreatment. For instance, the hydrogen
partial pressure is preferably between about 690 kPa and about
6,900 kPa, and more preferably between about 2,060 kPa and about
3,450 kPa. Moreover, the liquid hourly space velocity is preferably
between about 1 hr.sup.-1 and about 10 hr.sup.-1, more preferably
between about 0.5 hr.sup.-1 and about 6 hr.sup.-1, and most
preferably between about 1 hr.sup.-1 and about 5 hr.sup.-1.
[0125] Alternatively or in addition, the hydroprocessing may
comprise a hydrocracking step to convert heavy paraffins to lighter
paraffins. Methods of hydrocracking are well known in the art, and
hydrocracking of heavy distillate (such as wax) can include any
suitable method. The hydrocracking preferably takes place over a
platinum catalyst at temperatures from about 260.degree. C. to
about 400.degree. C. and at pressures from about 3,550 kPa to about
10,440 kPa. The heavy distillate is preferably fed to a
hydrocracker where its components are cracked into smaller
hydrocarbon molecules, wherein a good portion of the cracked
molecules are within the boiling range of diesel. The effluent of
the hydrocracker is preferably recycled to a fractionator so the
heavy hydrocarbons are recycled close to extinction.
[0126] Alternatively or in addition, the hydroprocessing may
comprise a hydroisomerization step to convert paraffins to more
branched paraffins, so as to generate a synthetic distillate with
at least one improved cold-flow property (such as lower pour
point). It may be desirable to hydroisomerize during the
hydrocracking step so as to form branched hydrocarbons, such as
convert linear paraffins to isomers of paraffins (isoparaffins or
branched paraffins); and/or convert monobranched paraffins to
dibranched paraffins. Isoparaffins are known to improve cold flow
properties in FT diesel, so increasing the relative amount of
branched hydrocarbons in FT diesel should yield a diesel with
decreased (improved) pour point. Paraffin isomerization catalysts
and processes that can be used for producing low pour point diesel
fuel can be found in U.S. Pat. Nos. 4,710,485; 4,589,138;
4,459,312; 5,149,421; 5,282,958, each of which is incorporated
herein by reference in its entirety. Additional isomerization
processes are described by Taylor and coworkers in Applied
Catalysis A: General (1994) vol. 119, pp. 121-138.
[0127] To further illustrate various illustrative embodiments of
the present invention, the following example is provided.
EXAMPLE
[0128] The interaction between the bulk modulus of compressibility
of various fuel samples and their effect on fuel injection timing
was examined. The fuels considered ranged from biodiesel B100 (as
methyl soyate, i.e., the methyl ester of soybean oil), unrefined
soybean oil, paraffinic solvent, Fischer-Tropsch derived diesel,
and ultra low sulfur diesel fuel. Both the impact on injection
timing and the variation in the bulk modulus of compressibility
were measured so that correlation between fuel composition, fuel
properties and injection timing could be observed and
quantified.
[0129] Two different experimental systems were used: a
high-pressure viscometer, capable of measuring the bulk modulus of
compressibility with the use of a pycnometer; and a highly
instrumented, single-cylinder direct injection (DI) diesel engine,
with an accompanying spray visualization chamber. The bulk modulus
of various fuels was measured, and corresponding measurements were
made of the impact of the fuel on the injection timing in the DI
diesel engine.
[0130] High-Pressure Viscometer
[0131] The high-pressure viscometer instrument was developed for
studies of the viscosity and bulk modulus of hydraulic fluids that
contained dissolved gases and described by J. A. O'Brien in his
1963 M.S. Thesis from Penn State University, PA, entitled "Precise
Measurement of Liquid Bulk Modulus". The operation for this device
was based on the following principle: when a fluid is exposed to
higher pressures, the fluid has a reduction in volume.
[0132] The isothermal bulk modulus of compressibility, B.sub.T, and
the isentropic bulk modulus of compressibility, B.sub.S, are
defined by Equations (3) and (4) respectively: 1 B T - v ( P v ) T
= ( P ) T ( 3 ) B S - v ( P v ) S = ( P ) S ( 4 )
[0133] where v is the specific volume and p is the density. The
isentropic bulk modulus of compressibility is related to the speed
of sound, a, by the Equation [5]: 2 a = ( P ) S ( 5 )
[0134] The experimental approach used in this experiment yielded a
measurement for the isothermal bulk modulus of compressibility,
B.sub.T, which will simply be referred to as B. The governing
Equation (6) for the calculation of bulk modulus is: 3 B = ( P - Po
) Vo ( Vo - V ) ( 6 )
[0135] where B is the isothermal bulk modulus, P is the measured
pressure, Po is atmospheric pressure, Vo is the volume of the
sample at atmospheric pressure and V is the volume at the new
pressure.
[0136] FIG. 5 shows a schematic diagram of the closed-bottom
pycnometer and housing used in these studies. The measurement
equipment 200 comprised a modified 21-R-30 Stainless Jerguson gauge
210 capable of handling pressures up to 4000 psi. Two panels with
viewing windows 220 allowed for viewing of the sample. Each window
glass had two gaskets, one on either side, to ensure a tight seal
on the chamber. For pressures in the range of 0-1000 psi, a direct
connection to a helium gas cylinder provided the necessary pressure
via helium inlet 230. For pressures above 2000 psi, a 4.5-liter
Aminco hydrogenation bomb (not shown) was filled with helium, and
oil was pumped into the bomb to achieve pressures up to 16,000 psi.
A constant temperature bath kept the pressure cell at a temperature
of 100.degree. F. Bulk modulus was measured via a change in height
in the capillary 240 within the pycnometer tube 250, as the
pressure in the cell was varied. The fuel sample was placed in
reservoir 260 of the pycnometer tube 250. N-Octadecane was used as
a calibration standard.
[0137] Direct Injection Diesel Engine and Spray Chamber
[0138] A Yanmar L40 AE D air cooled 4-stroke direct injection (DI)
diesel engine was coupled to an electric motor and motored at speed
and fuel consumption conditions that simulated the G2 test modes
from the ISO 8178-4.2 [ISO 8178: Reciprocating internal combustion
engines--Exhaust emissions measurement--Part 4. Test Cycles for
different engine applications. 1995, International Organization for
Standardization]. Only results from a load setting of 25% at 3600
RPM are presented here. The experimental system is shown
schematically in FIG. 6. The fuel consumption was measured by a
gravimetric method using an Ohaus Explorer balance, accurate to 0.1
g. The fuel injector 310 was removed from the cylinder head and
placed into a spray chamber 320 with visual access to the fuel
spray 330. The chamber 320 was positioned so that the original high
pressure fuel line 340 could be used without modification of
length, although it was necessary to bend the fuel line.
[0139] The spray timing was monitored with a light attenuation
method. A Uniphase 0.95 mW Helium-Neon laser 350 was positioned so
that a laser beam 360 intersected the fuel spray at the injector
orifice. During the spray event the laser was attenuated, changing
the output voltage and enabling a clear transition at both the
beginning and end of the spray. An AVL 364 shaft encoder mounted on
the engine crank shaft enabled 0.1 crank angle (CA) degree
resolution of the spray event. A data acquisition system 370
recorded the signals from the fuel line pressure sensor 380 and the
phototransistor 390 located at the end of the laser beam 360.
[0140] Fuel Samples
[0141] The tested fuel samples were a biodiesel fuel (B100), a
methyl soyate from World Energy, Chelsea, Mass.; an unrefined
soybean oil (soy oil) from Agricultural Commodities, Inc., New
Oxford, Pa.; Norpar.RTM.-13 (Norpar.RTM.), a normal paraffin
mixture from C.sub.11-C.sub.15 from ExxonMobil Chemicals, Houston,
Tex.; a Fischer-Tropsch diesel (FT diesel) from ConocoPhillips
Company, Houston, Tex.; a 15 ppm sulfur diesel fuel (BP-15) from
British Petroleum--Fuels Technology, Naperville, Ill.; and a
biodiesel/petroleum diesel blend (B20) consisting of methyl soyate
from World Energy and ultra low sulfur diesel fuel from British
Petroleum. Table 1 comprises properties of these fuel samples.
1TABLE 1 Properties of the fuel samples. Kinematic Density
viscosity at 15.degree. C., at 40.degree. C., Sulfur Boiling range*
Flash Cetane Fuels g/cm.sup.3 mm.sup.2/s (ppm) (.degree. C.) Point
(.degree. C.) number Norpar .RTM. 0.762 2.36 <5 105 (IBP) 97 na
(at 25.degree. C.) 117 (DP) FT diesel 0.778 2.5 <1 205-212 (5%)
72.7-74.4 83 325-339 (95%) BP-15 0.837 2.5 15 203 (10%) 63.8 50 343
(95%) B20 0.846 2.7 13 198 (10%) 66.1 52.5 334 (95%) B100 0.888 4.1
<1 369 (5%) 174 53 413 (95%) Soy Oil 0.91 31.3 na na >204 na
na: not available *all boiling points were determined by the ASTM
D-86 method, except for B100 where the ASTM D2887 (SimDis) method
was used.
[0142] The FT diesel was obtained by converting a synthesis gas
stream with a hydrogen-to-carbon monoxide molar ratio of about 2:1
over a Fischer-Tropsch cobalt-based catalyst in a slurry bubble
reactor at a temperature of about 210-215.degree. C. and a pressure
of about 450 psig (about 3200 kPa) so as to form a hydrocarbon
synthesis product. The hydrocarbon synthesis product was then
hydrotreated over a nickel-based catalyst so as to substantially
transform all of the olefins and oxygenates to paraffins; then
fractionated in an atmospheric distillation column to at least
obtain a FT diesel fraction.
[0143] The experiments were performed in order to examine two
separate issues with regard to fuel formulation and engine
emissions. The first was to study the difference in bulk modulus
between biodiesel fuels and diesel fuels and the resulting effect
on fuel injection timing. The second was the investigation of the
potential impact of the use of paraffinic fuels, such as
Fischer-Tropsch diesel fuels, on injection timing.
[0144] FIGS. 1 and 3 show results from the bulk modulus of
compressibility for diesel and biofuel blends, and the measurements
of injection timing for biofuel B100, baseline diesel, B20-FT blend
and the normal paraffin solvent (Norpar.RTM.). In FIG. 1, the bulk
modulus of B20, B100 and the soy oil are higher than that of the
baseline diesel fuel, consistent with the results reported in the
`Tat 2000 paper`. The bulk modulus of B20 was slightly above that
of the baseline diesel fuel BP-15. On the other end, the bulk
modulus of FT diesel, both FT diesel/biodiesel blends, and the
paraffinic solvent were lower than that of the baseline diesel fuel
(BP-15). Blends of 20% and 40 vol. % of (methyl soy) biodiesel and
a FT diesel therefore displayed a lower bulk modulus of
compressibility than the baseline diesel fuel, and should generate
lower NOx emissions that the baseline diesel.
[0145] A relative spray intensity of 0.2 was used as an indication
of the beginning of light scattering by the fuel spray, providing a
consistent means of quantifying the onset of the fuel spray.
Accordingly, using 0.2 relative spray intensity as an indication of
the start of fuel injection, FIG. 3 indicates that there was a 0.2
CA advance of fuel injection timing for the petroleum
diesel-biodiesel blend (B20), while there was an advance of 1.0 CA
with pure biodiesel (B100). The purely paraffinic solvent,
Norpar.RTM., retarded the fuel injection timing with the largest
retardation of 0.5 CA, while the B20-FT blend shows a retardation
of 0.1 CA in fuel injection timing. Norpar.RTM. also showed the
lowest bulk modulus of compressibility in FIG. 1. Since the B20-FT
blend with the synthetic FT diesel showed a retardation in fuel
injection timing (-0.1 CA), the B20-FT blend is expected to
generate less NOx emissions than the baseline fuel. On the other
end, the B20 blend with the ultra-low sulfur petroleum diesel
showed an advanced injection timing (+0.2 CA), the B20 blend is
expected to generate more NOx emissions than the baseline fuel.
[0146] In the present Example, the bulk moduli of blends of
biodiesel and FT diesel were examined to determine what blend ratio
would be equivalent in bulk modulus to the baseline diesel
(ultra-low sulfur diesel fuel BP-15) and what blend ratio would be
have a bulk modulus below that of the baseline diesel. Table 2
shows the respective bulk moduli extrapolated from FIG. 1 at 5 MPa,
15 MPa and 25 MPa for paraffinic solvent Norpar.RTM., FT diesel,
B20-FT, B40-FT, B20, B100 and soy oil.
2TABLE 2 Bulk modulus of compressibility at 100.degree. F. at
different pressures extrapolated from FIG. 1. B100 (methyl B20 with
BP-15 Pressure Soy Oil soyate) diesel diesel B40-FT60 B20-FT80 FT
diesel Norpar .RTM. 5 MPa 1980 1650 1500 1460 1430 1370 1350 1240
15 MPa 2070 1755 1605 1580 1555 1495 1455 1350 25 MPa 2150 1870
1730 1690 1670 1615 1555 1460
[0147] To illustrate the effect of biodiesel volume fractions on
the bulk moduli of the biodiesel/FT diesel blends, a plot of the
bulk moduli extrapolated at 15 MPa (and measured at 100.degree. F.)
taken from Table 2 of neat FT diesel, FT diesel/biodiesel blends
and neat biodiesel B100 versus the biodiesel volumetric fraction of
the blends, is shown in FIG. 2, wherein 0% represents neat FT
diesel and 100% represents neat B100. From FIG. 2, one can
visualize a blend of FT diesel and biodiesel which would lead to a
"NOx neutral" formulation with a biodiesel volume fraction that
would correspond to a bulk modulus of compressibility at 15 MPa to
be equal to about 1580 MPa, corresponding to the bulk modulus at 15
MPa for the baseline diesel. A B45-FT blend would correspond to a
bulk modulus of compressibility at 15 MPa of about 1580 MPa,
equivalent to that of the baseline diesel. Hence the B45-FT blend
comprised a "NOx neutral" biodiesel blend. Accordingly, the
biodiesel-FT diesel blends with less than 45% of biodiesel should
generate a reduced level of NOx emissions when used in a diesel
engine compared to conventional (crude derived) diesel
formulations.
[0148] The data in these tests also showed a trend of increasing
bulk modulus of compressibility with increasing density. As Table 3
shows, the density of the fuels considered here correlated directly
with the bulk modulus of compressibility.
3TABLE 3 Fuel injection timing, bulk modulus of compressibility at
1000 psi and 100.degree. F., and specific gravity of various fuels.
Bulk Modulus Crank Angle* for at 1000 psi SOI Relative to and
100.degree. F., BP-15 MPa Specific Gravity Norpar .RTM. -0.5 1262
0.762 FT diesel -0.5 1373 0.778 B20-FT -0.1 1390 nd BP-15 0 1477
0.837 B20** +0.2 1520 0.846 Soy oil 16 vol % +0.3 1579 0.852 B100**
+1.0 1668 0.888 Soy oil nd 1996 0.91 *A positive (+) Crank Angle
(CA) value represents an advance in injection timing, whereas a
negative (-) CA value represents a retardation in injection timing.
**B100 is methyl soyate and B20 comprises 20 vol % of B100.
[0149] The NOx emissions trends for the speciated biodiesel
constituents and various biodiesel feedstocks shown in the
`McCormick 2001 paper` can be explained, in light of the present
work, on the basis of the variation of the bulk modulus of the
fuels, consistent with the observations of Van Gerpen and
co-workers, such as are disclosed in the `Monyem paper` and in the
`Tat 2000 paper`. These same observations have relevance to the
formulation of reformulated diesel fuels, FT diesel fuels,
biodiesel fuels (B20, B100, etc.) and blends thereof.
[0150] The present Example demonstrated that the higher bulk
modulus of compressibility of biodiesel (specifically a methyl
ester of soybean oil) led to advanced injection timing. This
advanced injection timing has been shown in the literature to
contribute to the well-documented NOx emissions increase with the
use of biodiesel fuel. An opposite trend, a retarding of injection
timing, was observed with paraffinic fuels because they have a
lower bulk modulus of compressibility than conventional diesel
fuels. This supports the observation that paraffinic fuels such as
Fischer-Tropsch diesel fuels yield lower NOx emissions. Thus, the
observations of the biodiesel "NOx effect" reported in the
literature can be attributed to variations in the bulk modulus of
compressibility of the fuel or fuel blend, and these effects
correlate for biofuels and paraffinic fuels quite well with fuel
density.
[0151] The embodiments set forth herein are merely illustrative.
Many varying and different embodiments may be made within the scope
of the present inventive concept, including equivalent structures
hereafter thought of, permutations, substitutions, or combinations
of features from the embodiments herein detailed in accordance with
the descriptive requirements of the law. Many modifications may be
made as well in these embodiments. Because of these reasons, it is
to be understood that the details herein are to be interpreted as
illustrative and not in a limiting sense. Although the present
invention and its advantages have been described in detail, it
should be understood that various changes, substitutions and
alterations may be made herein without departing from the spirit
and scope of the invention as defined by the appended claims.
* * * * *