U.S. patent application number 13/552702 was filed with the patent office on 2014-01-09 for aviation gas turbine fuel with improved low temperature operability.
This patent application is currently assigned to EXXONMOBIL RESEARCH AND ENGINEERING COMPANY. The applicant listed for this patent is Roger G. Gaughan, Dennis H. Hoskin, Paul P. Wells, Krystal B. Wrigley. Invention is credited to Roger G. Gaughan, Dennis H. Hoskin, Paul P. Wells, Krystal B. Wrigley.
Application Number | 20140007498 13/552702 |
Document ID | / |
Family ID | 46690690 |
Filed Date | 2014-01-09 |
United States Patent
Application |
20140007498 |
Kind Code |
A1 |
Wells; Paul P. ; et
al. |
January 9, 2014 |
AVIATION GAS TURBINE FUEL WITH IMPROVED LOW TEMPERATURE
OPERABILITY
Abstract
The addition of biodiesel to petroleum-based kerosene jet fuels
in very low concentrations can lower the temperature at which
crystals appear in the fuel. The fuels can comprise a blend of a
hydrocarbon base fuel component and, for example, up to 1000 ppm,
v/v of the total fuel, of a biodiesel component comprising a lower
alkyl ester of a fatty acid of natural origin having from 8 to 24
carbon atoms; these blends can be characterized by improved low
temperature flow properties, especially of Cloud Point (ASTM D
2500), which can be lower than that of the petroleum fuel component
without the alkyl ester, even in the presence of dissolved water up
to the saturation level.
Inventors: |
Wells; Paul P.; (Mullica
Hill, NJ) ; Wrigley; Krystal B.; (Turnersville,
NJ) ; Hoskin; Dennis H.; (Westampton, NJ) ;
Gaughan; Roger G.; (Sewell, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wells; Paul P.
Wrigley; Krystal B.
Hoskin; Dennis H.
Gaughan; Roger G. |
Mullica Hill
Turnersville
Westampton
Sewell |
NJ
NJ
NJ
NJ |
US
US
US
US |
|
|
Assignee: |
EXXONMOBIL RESEARCH AND ENGINEERING
COMPANY
Annandale
NJ
|
Family ID: |
46690690 |
Appl. No.: |
13/552702 |
Filed: |
July 19, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61509817 |
Jul 20, 2011 |
|
|
|
Current U.S.
Class: |
44/388 |
Current CPC
Class: |
C10L 1/19 20130101; C10L
2270/04 20130101; C10G 2400/08 20130101; C10L 2200/043 20130101;
Y02E 50/13 20130101; Y02E 50/10 20130101; C10L 2200/0476 20130101;
C10L 1/026 20130101; C10L 1/02 20130101; C10L 10/14 20130101; Y02T
50/678 20130101; C10G 2300/304 20130101; C10L 1/125 20130101 |
Class at
Publication: |
44/388 |
International
Class: |
C10L 10/14 20060101
C10L010/14 |
Claims
1. A petroleum-based aviation gas turbine fuel comprising a blend
of a hydrocarbon base petroleum fuel component and a sufficient
non-zero amount, up to 1% by volume of the total fuel, of a lower
alkyl ester of a fatty acid of natural origin having from 8 to 24
carbon atoms, such that the blend exhibits a Cloud Point (ASTM D
2500) at least 1.degree. C. lower than that of the petroleum fuel
component without the alkyl ester.
2. An aviation gas turbine fuel according to claim 1, in which the
amount of the lower alkyl ester is from 10 to 1000 ppm, v/v of the
total fuel, and the blend exhibits a Cloud Point (ASTM D 2500) at
least 3.degree. C. lower than that of the petroleum fuel component
without the alkyl ester.
3. An aviation gas turbine fuel according to claim 2, in which the
amount of the lower alkyl ester is from 10 to 50 ppm, v/v of the
total fuel, and the blend exhibits a Cloud Point (ASTM D 2500) at
least 3.degree. C. lower than that of the petroleum fuel component
without the alkyl ester.
4. An aviation gas turbine fuel according to claim 2, in which the
amount of the lower alkyl ester is from 100 to 300 ppm, v/v of the
total fuel, and the blend exhibits a Cloud Point (ASTM D 2500) at
least 3.degree. C. lower than that of the petroleum fuel component
without the alkyl ester.
5. An aviation gas turbine fuel according to claim 1, in which
lower alkyl ester comprises a methyl ester of a C.sub.8 to C.sub.22
fatty acid of natural origin.
6. An aviation gas turbine fuel according to claim 5, in which
lower alkyl ester comprises a methyl ester of a C.sub.12 to
C.sub.22 fatty acid of natural origin.
7. An aviation gas turbine fuel according to claim 6, in which
lower alkyl ester comprises a methyl ester of a C.sub.12 to
C.sub.18 fatty acid of natural origin.
8. An aviation gas turbine fuel according to claim 5, in which
lower alkyl ester comprises a methyl ester of a fatty acid derived
from rapeseed oil.
9. An aviation gas turbine fuel according to claim 5, in which
lower alkyl ester comprises a methyl ester of a fatty acid derived
from soybean oil.
10. An aviation gas turbine fuel according to claim 5, in which
lower alkyl ester comprises a methyl ester of a fatty acid derived
from palm oil.
11. An aviation gas turbine fuel according to claim 5, in which
lower alkyl ester comprises a methyl ester of a fatty acid derived
from tallow.
12. An aviation gas turbine fuel according to claim 5, in which
lower alkyl ester comprises a blend of methyl esters of fatty acids
derived from rapeseed oil, soybean oil, palm oil, and tallow.
13. An aviation gas turbine fuel according to claim 1, which
conforms to the specification for Jet A and/or Jet A-1 (Def. Stan.
91-91 and/or ASTM D1655).
14. An aviation gas turbine fuel according to claim 1, which
conforms to the specification for JP-5 (MIL-T-5624 N).
15. An aviation gas turbine fuel according to claim 1, which
conforms to the specification for JP-8 (MIL-T-83133C).
16. An aviation gas turbine fuel according to claim 1, which
contains a total amount of water, wherein the petroleum component
has a water saturation level, and wherein the total amount of water
in the fuel is less than or equal to said water saturation
level.
17. An aviation gas turbine fuel according to claim 1, which
contains free water in an amount up to 30 ppm, v/v of the total
fuel.
18. An aviation gas turbine fuel according to claim 1, which has a
Freeze Point (ASTM D5972) within 1.degree. C. of a Freeze Point of
the petroleum fuel component without the alkyl ester.
19. An aviation gas turbine fuel according to claim 1, which has a
Cold Filter Plugging Point (ASTM D6371) within 1.degree. C. of a
Cold Filter Plugging Point of the petroleum fuel component without
the alkyl ester.
20. An aviation gas turbine fuel according to claim 1, which has a
Cloud Point (ASTM D2500) at least 5.degree. C. lower than a Cloud
Point of the petroleum fuel component without the alkyl ester.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 61/509,817, filed Jul. 20, 2011, which is
incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to fuels useful in aviation gas
turbine engines and more particularly, to aviation gas turbine
fuels with improved low temperature operability
characteristics.
BACKGROUND OF THE INVENTION
[0003] Kerosene type fuels (kerojet) are well-established for use
in aviation gas turbines, typically going under the designations
such as Jet A, Jet A-1, JP-5, JP-8, NATO F-34, or NATO F-44. The
various specifications impose a number of different requirements on
the respective fuels, including flash point, distillation, maximum
aromaties (coupled with Smoke Point), viscosity (-20.degree. C.),
sulfur content, net heat of combustion, and density. Aircraft which
fly at high altitude or encounter extremely cold environments have
the potential for fuel freezing and, consequently, catastrophic
failure of the fuel system; the low temperature properties of the
fuel are therefore important factor in acceptability, and a number
of tests have been developed to quantify the behavior of kerosene
fuels at the low temperatures typically encountered in aviation
use. The Cloud Point (ASTM D 2500) test measures the temperature at
which paraffin crystals start to precipitate and therefore provides
an indication of the temperature at which incipient system plugging
problems arise. Low Cloud Point is therefore highly desirable in a
kerosene jet fuel.
[0004] In recent years, energy crises and their consequent increase
in prices have led to increased interest in alternative fuels, for
example, Fischer-Tropsch liquids, coal liquefaction products, and
bio-derived fuels. One type of bio-fuel which has received
significant interest in recent years as a possible alternative to
conventional petroleum diesel is biodiesel, and this has also been
considered as an alternative aviation turbine fuel, in view of its
character similar to petroleum-derived middle distillates, such as
petroleum diesel (petrodiesel). Biodiesel is generally taken to be
an ester produced by the transesterification of triglycerides found
in naturally occurring oils and fats. Various crops and animal
sources are used in different parts of the world, depending on
local availability: soybean oil is widely used in the U.S. and in
Europe; and rapeseed oil and palm oil or coconut oil in Asia.
Tallow (animal fat) is also a source of triglycerides which have
been converted to lower alkyl esters for biodiesel. Mixtures of oil
may also be used. The lower alcohol normally used to effect the
transesterification is methanol although other alcohols, such as
ethanol, propanol, butanol, etc., may also be used. During the
transesterification, the triglycerides of the long chain fatty
acids in the natural oil are converted to fatty acid esters of the
lower alcohol used in the esterification process with glycerol as a
by-product. The fatty acid methyl ester products are generally
referred to as FAMEs (Fatty Acid Methyl Esters) and include such
classes as tallow methyl esters (TME), soybean methyl esters (SME),
rapeseed methyl esters (RME), and palm oil methyl esters (PME).
[0005] Studies have been made on the use of biodiesel as an
alternative jet fuel, and it has been concluded that, although
significant technical and logistical hurdles need to be overcome,
the task is not insurmountable and no single issue makes biofuel
unfit for aviation use ("Alternative Fuels and Their Potential
Impact on Aviation", NASA Report TM-2006-214365, Daggett et al.).
The cost of bio-derived fuels is a major logistical consideration:
the 2003 report from the Imperial College Centre for Energy Policy
and Technology ("The Potential for Renewable Energy Sources in
Aviation", Saynor et al, with rapeseed methyl esters projected to
cost from US$33.5/GJ to US$52.6/GJ as compared to approximately
US$4.6/GJ for petroleum kerojet. The greatest technical problem, as
noted in the NASA report, with biodiesel is its need for warm
temperatures: at normal flight temperatures, bio-derived jet fuel
tends to freeze, and, for this reason, the amount of bio-derived
fuel that can be blended with petroleum-based fuels is normally
limited, typically to 10-20% of the blend. Blended with kerosene,
biodiesel is known to raise the fuel's cloud point significantly.
According to the Imperial College report, the addition of just 10
wt % biodiesel to kerojet raises the cloud point from -51.degree.
C. to -29.degree. C., a level which is unacceptable for the
military JP8, which requires fuels to operate at -47.degree. C.
[0006] The presence of water in the fuel affects the Cloud Point,
since not only do wax crystals appear at the Cloud Point but also
ice crystals are prone to precipitate at even higher temperatures.
A great deal of care is therefore taken to ensure petroleum
products are transported throughout the distribution system as dry
as possible and that they are essentially dry when loaded onto the
plane. For example, warm, potentially wet product from the refinery
is allowed to cool and settle before transport, thereby reducing
the amount of dissolved and/or finely dispersed free water. Storage
tanks are regularly sumped to remove any water bottoms. Floating
suction is an industry best practice and helps ensure dry product
enters the distribution system. Even with these procedures in
place, dissolved water can and does come out of solution as ambient
temperature is reduced. The resulting free water can then cause
corrosion, encourage microbiological growth, or freeze and block
downstream fuel filters. Water is normally removed by passing the
jet fuel through filter/coalescer and separator systems, normally a
filter/coalescer cartridge and a separator cartridge specified by
API/IP 1581 3.sup.rd edition or 5.sup.th edition (Category C,
Category M, or Category M100) at several points in the fuel
distribution system, usually at least when the fuel is transferred
into and out of airport storage facilities. Into-plane jet fuel
water content standards are either 15 ppm v/v (ATA-103) or 30 ppm
v/v (IATA), as cited in the airline operator's handling standards,
where ATA-103 is commonly cited in the U.S. and IATA elsewhere
(outside the former Soviet Union and China).
[0007] Anti-icing agents are currently used to improve the low
temperature performance by reducing the incidence of solids
formation. For example, di-ethylene glycol monomethyl ether
(DiEGME) is added to the military jet fuel JP-8. DiEGME, however,
is expensive, added at 0.15 vol % (or 1,500 ppm v/v), and is
incompatibile with filter monitors commonly used in the
distribution system to remove free water from the fuel as it is
loaded onto the plane.
[0008] Various proposals for improving the low temperature
performance of bio-derived distillate range fuels have been made.
U.S. Patent Application Publication No. 2006/0229222 relates to
methods for improving the low temperature storage and performance
properties of fatty acids and their derivatives, as well as of
composition containing them, by the use of stabilizers selected
from branched chain fatty acids, cyclic fatty acids, and
polyamides. Jet fuels and diesel are mentioned as blend components
for fatty acid compositions.
[0009] U.S. Patent Application Publication No. 2008/0163542
discloses blends of petroleum based fuels with renewable fuels to
enhance the low temperature operability of the blends. Various
performance indices, such as the Cold Filter Plugging Point, the
Low Temperature Flow Test, Pour Point, and Cloud Point, are taken
as measures of the low temperature performance characteristics of
fuels such as kerosene-type aviation fuels, e.g., JP-5, JP-8, Jet
A, and Jet A-1. The bio-derived component in the blend is stated to
be no more than 50% v/v in typical cases and more typically up to
35% v/v; very low proportions down to 0.5% are mentioned but with
no advantage shown for such blends.
[0010] U.S. Patent Application Publication No. 2010/0005706
discloses fuel oil compositions based on blends of renewable and
petroleum fuels with additives to enhance the resistance to forming
particulates during low temperature storage.
[0011] U.S. Patent Application Publications Nos. 2010/00058651 and
2011/0023352 disclose mixtures of fatty acid methyl esters useful
as biofuels such as biodiesel and which are stated to have improved
properties both at low and high temperatures.
[0012] Trial flights with blended jet fuels have been reported by
commercial airlines including Air New Zealand, Japan Airlines, and
military units such as the U.S. Air Force and U.S. Navy.
SUMMARY OF THE INVENTION
[0013] As noted above, biofuels, especially biodiesel are generally
considered to create low temperature performance problems. We have
now found, however, that the addition of a relatively small amount
of biodiesel, a widely available and inexpensive material, to
petroleum-based kerosene jet fuels can facilitate a lowering in the
temperature at which crystals can appear in the fuel. This property
is quite unexpected in view of the known propensities of these
materials.
[0014] According to the present invention, petroleum-based aviation
gas turbine fuels comprise a blend of a hydrocarbon base petroleum
fuel component and a non-zero amount up to about 1 percent by
volume of the total fuel, of a biodiesel comprising a lower alkyl
ester of a fatty acid of natural origin having from 8 to 24 carbon
atoms; these blends can advantageously be characterized by a Cloud
Point (ASTM D 2500) lower than that of the petroleum fuel component
without the alkyl ester.
[0015] The amount of the lower alkyl ester is usually less than the
maximum 1 vol % noted herein, e.g., from 10 to 1000 ppm v/v, from
10 to 500 ppm v/v, from 10 to 50 ppm v/v, from 50 to 500 ppm v/v,
or in certain cases from 100 to 300 ppm v/v of the total fuel. The
bulk of the fuel can thus typically comprise or be a conventional
petroleum-based kerojet, e.g., having a middle distillate boiling
range (initial to final boiling point or optionally either a T2 to
T98 range or a T5 to T95 range), such as from 180.degree. C. to
350.degree. C.
[0016] The fuel can generally be manufactured to comply with
established aviation turbine fuel standards according to the user
and thus should generally meet the specifications for Jet A and/or
Jet A-1 (Def. Stan. 91-91 and/or ASTM D1655), JP-5 (NATO
F-44)(MIL-T-5624 U), and/or JP-8 (NATO F-35)(MIL-T-83133E). Free
water (i.e., water present as discrete droplets within the fuel,
with droplet size typically varying from .about.1 micron to
.about.30 microns, depending upon the presence of optional
surfactants) may be present in fuel when loaded on-plane in the
amounts allowed by the relevant specification, e.g., either 15 ppm
v/v under ATA-103 and/or 30 ppm v/v (IATA), according to the
operator's handling standards, as determined by API/EI 1581
(formerly API/IP 1581). GOST specifications can generally apply in
Russia, China, and FSU countries. Surprisingly, it has been found
that the addition of the exceedingly small amounts of biodiesel
(e.g., as low as about 10 ppm v/v of a lower alkyl ester) can
result in a lowered temperature for crystal formation in the
petroleum fuel component, even when the total amount of dissolved
water approaches the saturation level (typically about 75 ppm v/v
at ambient temperature) in the petroleum component.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0017] The major component of the present fuel blends can
advantageously include or be a hydrocarbon middle distillate.
Though typically the hydrocarbon middle distillate can be derived
solely or mostly from mineral (non-renewable) sources (e.g., crude
oil, shale oil, and the like), additionally or alternately at least
a portion of the hydrocarbon middle distillate can be derived from
a renewable (non-mineral) source (e.g., plants and/or animals, such
as vegetables/crops, domesticated land/air animal, aquatic
organisms including fish and/or algae, and/or other uni- or
multi-cellular organisms capable of producing the appropriate
hydrocarbon molecules and/or precursors). The hydrocarbon middle
distillate can have certain desired boiling point characteristics,
e.g., an initial to final boiling point range from 180.degree. C.
to 350.degree. C., respectively. In certain embodiments, though,
the hydrocarbon middle distillate may have a relatively small
proportion of molecules whose boiling points are outside that
desired range, such that it may be more universally applicable to
describe the T1 to T99 boiling point range, the T2 to T98 boiling
point range, or the T5 to T95 boiling point range, which can
collectively, or each individually, range from 180.degree. C. to
350.degree. C. As used herein, the expression "T[number]", with
reference to a composition, shall be understood to refer to a
situation where approximately [number] percent by weight of the
composition has a boiling point (under atmospheric pressure). For
instance, a composition has a T10 boiling point of about
200.degree. C. if approximately 10% by weight of the composition
has boiled at a temperature of about 200.degree. C.
[0018] The volatility and other characteristics of the present fuel
blends can be selected according to the fuel specification, e.g.,
by the specifications for Jet A, Jet A-1, JP-5, and/or JP-8,
according to end user. Thus, for example, with Jet A and Jet A-1, a
maximum T10 boiling point is typically 185.degree. C., and a
maximum final boiling (end) point is typically 340.degree. C. (Sim.
Dis., ASTM D 2887). Also for Jet A and Jet A-1, the minimum Flash
Point (ASTM D 56 or 3828) is typically 38.degree. C., with similar
specifications for JP-8. For JP-5, the maximum final boiling (end)
point is typically 330.degree. C. (ASTM D 2887), and the minimum
Flash Point is typically 60.degree. C. The hydrocarbon middle
distillate (fuel) component may be manufactured by any suitable
(such as conventional) methods known in the art.
[0019] The biodiesel component can be a renewable fuel of natural
origin, typically having a middle distillate boiling range. As used
herein, the phrase "of natural origin", with reference to a fatty
acid herein, should be understood to mean not chemically
synthesized by the hand of man. For clarification, regarding fatty
acids, this means that the acyl portion of the fatty acid (i.e.,
the carbonaceous portion of the fatty acid, which constitutes all
the carbons in the chain, including the carbon and oxygen atoms
from the carbonyl bond, optionally, but not necessarily, including
the acid oxygen and hydrogen atoms), whether existing in a free
acid, acid salt, and/or (tri-)glyceride form, originates from an
organism. The organism may be either naturally occurring or
genetically modified, naturally and/or by man's intervention, and
still be considered "of natural origin", so long as the acyl
portion of the fatty acid is produced by and/or through the
organism.
[0020] Biodiesel is described officially by the National Biodiesel
Board (USA) according to ASTM D 6751 as a fuel comprised of
mono-alkyl esters of long chain fatty acids derived from vegetable
oils or animal fats; European Standard EN 14214 describes the
requirements and test methods for FAME biodiesel. Biodiesel is
typically produced by a reaction of a vegetable oil or animal fat
with a lower alcohol such as methanol or ethanol, optionally in the
presence of a catalyst, to yield the desired lower mono-alkyl
esters and glycerin, which can be advantageously removed as a
by-product. As used herein, the term "lower", only as it refers to
alcohols and alkyl esters, should be understood to mean 1 to 5
carbon atoms, for example 1 to 4 carbon atoms or 1 to 2 carbon
atoms.
[0021] Biodiesel molecules can be blended with petroleum based
diesel fuels for use in existing diesel engines, usually with
little or no modification to the engine or fuel systems, and can
thus be seen as distinct from the vegetable and waste oils that
have been suitably modified to be used in diesel engines. Biodiesel
molecules are also capable of being blended with conventional
petroleum-derived kerojet to make a fuel useful in aviation gas
turbines when the appropriate specifications are met.
[0022] The vegetable/crop oils conventionally used in the
manufacture of biodiesel can vary, often according to local
availability: rapeseed and soybean oils can be commonly used, with
soybean oil alone accounting for about ninety percent of all
production in the U.S. Vegetable/Crop oils can additionally or
alternately be obtained from corn, castor, olive, linseed, mustard,
peanut, safflower, sunflower, and/or the like, as well as from
other sources such as tall oil and/or field pennycress; in tropical
zones, oils such as palm oil, coconut oil, hemp oil, honga oil,
jatropha, and/or the like may be favored. Waste vegetable oil
(WVO), or the oil remaining after use of the oil in food
preparation, can additionally or alternately constitute a potential
source. Animal fats, such as tallow (beef fat), lard (hog fat),
chicken fat, duck fat, fish oil, and the like, are farther
additionally or alternately potential sources. The vegetable/crop
oil sources can be preferred over land animal/fowl fat sources, for
example, particularly in situations where low temperature
properties are important. However, in situations where relatively
small amounts of biodiesel component are used in the present
blends, the relative impact of such molecules on the low
temperature properties of the present blends can be small or
insignificant, in which situations there may be no particular
biodiesel source preference. Of course, combinations of various
(natural) oils/fats are contemplated.
[0023] The selected (natural) oils/fats can be converted to their
corresponding mono-esters, e.g., by a transesterification process
using a lower alkanol as the esterifying agent. Methanol is
normally preferred to make the methyl esters of the fatty acid
components (Fatty Acid Methyl Ester--FAME), as it is the cheapest
lower alcohol available, although ethanol can be used to produce an
ethyl ester (Fatty Acid Ethyl Ester--FAEE) that can still be useful
as biodiesel; higher alcohols, e.g., n-propanol, isopropanol,
and/or butanols, even up to C.sub.6 or C.sub.8 alkanols, have also
been used. Using increasingly higher carbon number alcohols can
often improve the cold flow properties of the resulting alkyl
ester, but generally at the cost of an increasingly less efficient
and more costly transesterification reaction. Heat, as well as an
acid or a base, can be used to catalyze the reaction. The
predominant method for commercial-scale biodiesel is the
base-catalyzed process, as it is seen as the most economical
process for treating virgin vegetable oils, requiring relatively
low temperatures and pressures and producing as high as 98+%
conversion yield, if the starting oil is relatively low in moisture
and free fatty acid content. Biodiesel produced from animal fats
and other sources or by other methods may work better with acid
catalysis, which can be slower.
[0024] The fatty acids from which preferred esters can be made can
be saturated (containing no carbon-carbon double bonds) and/or
unsaturated (containing one or more carbon-carbon double bonds) and
can have acyl chain lengths (pre-esterification acid-equivalent
numbers of carbons) ranging from 8 to 24 carbons, for example, 8 to
22 carbons, 10 to 22 carbons, 12 to 22 carbons, typically
predominantly (i.e., more than 50% by weight) 12 to 18 carbons or
14 to 18 carbons. Non-limiting examples of fatty acids can include,
but are not limited to, caprylic acid (C8:0), capric acid (C10:0),
lauric acid (C12:0), myristic acid (C14:0), palmitic acid (C16:0),
palmitoleic acid (C16:1), sapienic acid (C16:2), stearic acid
(C18:0), oleic acid (C18:1), linoleic acid (C18:2), linolenic acid
(C18:3), arachidic acid (C20:0), eicosenoic acid (C20:1),
eicosadienoic acid (C20:2), mead acid (C20:3), arachidonic acid
(C20:4), eicosapentanoic acid (C20:5), behenic acid (C22:0) erucic
acid (C22:1), lignoceric acid (C24:0), nervonic acid (C24:1), and
the like, and obviously combinations thereof. Unsaturated acids,
typically obtainable from canola, linseed, camelina, mustard,
soybean oils, and/or other vegetable/crop oils can be preferred in
certain embodiments, e.g., for their improved flow properties.
[0025] In the present fuel compositions, the biodiesel component
can be advantageously used in relatively small (additive) amounts,
but in amounts still sufficient to contribute a significant effect
on the low temperature flow properties of the combination/blend of
the biodiesel component and the hydrocarbon (middle distillate)
fuel component, especially with reference to the blend Cloud Point
(ASTM D 2500). The addition of the biodiesel can advantageously
have an insignificant, or no observable, effect on other low
temperature properties, such as Freeze Point (ASTM D5972) and Cold
Filter Plugging Point (ASTM D6371), e.g., maintaining the values of
these within 2.degree. C., typically within 1.degree. C., of the
respective low temperature property value for the same fuel/blend
when no biodiesel is present. When biodiesel is present in the
fuel/blend in amounts up to 1000 ppm v/v, the Cloud Point has been
found to be at least 1.degree. C. lower than that of the
unadditized composition, typically at least 3.degree. C. lower, for
example at least 5.degree. C. lower, or at least 8.degree. C.
lower, than for the same fuel/blend without the biodiesel
component. This effect can be observed in certain circumstances
even with significant amounts of dissolved water present, e.g., up
to the saturation level of water in the fuel/blend (kerojet fuel
saturated at room temperature at sea level can hold .about.75 ppm
v/v dissolved water in solution, which can decrease as
temperature/pressure decrease).
[0026] Additionally or alternately, the present invention can
include one or more of the following embodiments.
Embodiment 1
[0027] A petroleum-based aviation gas turbine fuel comprising a
blend of a hydrocarbon base petroleum fuel component and a
sufficient non-zero amount, up to 1% by volume of the total fuel,
of a lower alkyl ester of a fatty acid of natural origin having
from 8 to 24 carbon atoms, such that the blend exhibits a Cloud
Point (ASTM D 2500) at least 1.degree. C. lower than that of the
petroleum fuel component without the alkyl ester.
Embodiment 2
[0028] An aviation gas turbine fuel according to embodiment 1, in
which one or more of the following is satisfied: the amount of the
lower alkyl ester is from 10 to 1000 ppm, v/v of the total fuel;
the amount of the lower alkyl ester is from 10 to 50 ppm, v/v of
the total fuel; the amount of the lower alkyl ester is from 100 to
300 ppm, v/v of the total fuel; and the blend exhibits a Cloud
Point (ASTM D 2500) at least 3.degree. C. lower than that of the
petroleum fuel component without the alkyl ester.
Embodiment 3
[0029] An aviation gas turbine fuel according to either of
embodiments 1-2, in which the lower alkyl ester comprises one or
more of the following: a methyl ester of a C.sub.8 to C.sub.22
fatty acid of natural origin; a methyl ester of a C.sub.12 to
C.sub.22 fatty acid of natural origin; a methyl ester of a C.sub.12
to C.sub.18 fatty acid of natural origin; a methyl ester of a fatty
acid derived from rapeseed oil; a methyl ester of a fatty acid
derived from soybean oil; a methyl ester of a fatty acid derived
from palm oil; a methyl ester of a fatty acid derived from tallow;
and a blend of methyl esters of fatty acids derived from rapeseed
oil, soybean oil, palm oil, and tallow.
Embodiment 4
[0030] An aviation gas turbine fuel according to any one of the
previous embodiments, which conforms to one or more of the
following specifications: Jet A (Def. Stan. 91-91); Jet A-1 (ASTM
D1655); JP-5 (MIL-T-5624 N); and JP-8 (MIL-T-83133C).
Embodiment 5
[0031] An aviation gas turbine fuel according to any one of the
previous embodiments, which contains a total amount of water,
wherein the petroleum component has a water saturation level, and
wherein the total amount of water in the fuel is less than or equal
to said water saturation level.
Embodiment 6
[0032] An aviation gas turbine fuel according to any one of the
previous embodiments, which contains free water in an amount up to
30 ppm, v/v of the total fuel.
Embodiment 7
[0033] An aviation gas turbine fuel according to any one of the
previous embodiments, wherein the fuel exhibits one or more of the
following: a Freeze Point (ASTM D5972) within 1.degree. C. of a
Freeze Point of the petroleum fuel component without the alkyl
ester; a Cold Filter Plugging Point (ASTM D6371) within 1.degree.
C. of a Cold Filter Plugging Point of the petroleum fuel component
without the alkyl ester; and a Cloud Point (ASTM D2500) at least
5.degree. C. lower than a Cloud Point of the petroleum fuel
component without the alkyl ester.
EXAMPLES
Example 1
[0034] A dried kerojet fuel (Jet A) was prepared by exposure to a 4
A molecular sieve dessicant; this treatment has been shown to be
very effective at removing solublized water. The Karl Fisher
(D6304) water content of the dried Jet A sample was about 38 ppm
w/w via Procedure A.
[0035] A sample of the Jet A fuel (not dried) was saturated by
placing it in an epoxy-lined 5-US gallon (.about.19 L) can,
containing a .about.1 L heel of distilled water, then sparging wet
nitrogen over the headspace. Sparging was conducted overnight (for
at least .about.10 hours) to fully saturate the sample.
[0036] The Cloud Points of the saturated fuel and the dried fuel
were about -51.degree. C. and about -60.degree. C., respectively.
Even though the freezing point of water is significantly higher
(.about.0.degree. C.), the water content apparently affected the
results, causing Cloud Point results to be noticeably higher for
the water-saturated fuel than for the dried fuel.
[0037] To determine the effect of biodiesel concentration on low
temperature operability, a sample of the saturated Jet A was
additized with different concentrations (.about.50 ppm v/v,
.about.100 ppm v/v, .about.250 ppm v/v, and .about.400 ppm v/v) of
a FAME mixture. The FAME mixture was prepared from equal volumes of
soybean oil methyl ester (SME), rapeseed oil methyl ester (RME),
palm oil methyl ester (PME), and tallow methyl ester (TME). The
additized samples were then submitted for testing by the procedures
of ASTM D2500 (Cloud Point), ASTM D5972 (Freeze Point), and ASTM
D6371 (Cold Filter Plugging Point). The results are summarized in
Table 1 together with the result of the dried fuel for
comparison.
TABLE-US-00001 TABLE 1 Blend. No. 1 2 3 4 5 6 FAME, ppm 0 50 100
250 400 0 v/v Saturated Balance Balance Balance Balance Balance --
Jet A Dry Jet A -- -- -- -- -- Balance Freeze Point, -58.1 -58.0
-57.9 -58.0 -57.9 -- .degree. C. Cloud Point, -51 -59 <-60
<-60 -59 -60 .degree. C. CFPP, .degree. C. -61 -60 -60 -60 -60
-- (D6371*) *The ASTM method indicates that measurements should
stop at -51.degree. C.; however, the samples in this Example were
tested until CFPP was determined, for better comparison, even
though these values required measuring CFPP at temperatures below
-51.degree. C.
[0038] Interestingly, it can be seen from Table 1 that the water
content within the jet fuel clearly affected Cloud Point results
with virtually no effect on the other two low-temperature
properties measured, namely Freeze Point and CFPP, Indeed, addition
of only .about.50 ppm v/v biodiesel appeared to be enough to engage
the water and significantly lower the cloud point of the fuel to a
value comparable to that of the reference blend produced with dried
fuel. Without being bound by theory, it appeared that the FAME
component interacted somehow with whatever water was bound within
the hydrocarbon jet fuel, with the end result being a measurably
lower Cloud Point.
[0039] ASTM D2500-09 lists two different sets of repeatability (r)
and reproducibility (R) levels depending upon sample type (i.e.,
one set for petroleum products and another set for biodiesel
blends). The levels are slightly greater for petroleum products
(r=2.degree. C. and R=4.degree. C.). Applying these more stringent
levels, the cloud point reproducibility bands for the Blend Nos. 1
and 2 might just intersect at about -55.degree. C. The
reproducibility bands for Blend Nos. 1 and 3, as well Blend Nos. 1
and 6, however, would not overlap.
Example 2
[0040] A similar series of samples was prepared using Jet-A in its
"as-received" or "as is" condition, containing about 54 ppm w/w
water by the Karl Fisher (D6304) Procedure A (representing less
than the saturation amount of water, typically .about.75 ppm v/v or
.about.93 ppm w/w). The FAME additive was then added to the "as is"
jet fuel in the same relative amounts as in Example 1, and the
Freeze Point (D5972), Cloud Point (D2500), and Cold Filter Plugging
Point (ASTM D6371) were determined. The results are given in Table
2 below.
TABLE-US-00002 TABLE 2 Blend No. 7 8 9 10 11 FAME, ppm v/v 0 50 100
250 400 "As-Is" Jet A Balance Balance Balance Balance Balance
Freeze Pt., .degree. C. (D5972) -58.3 -58.1 -58.0 -58.1 -58.1 Cloud
Pt., .degree. C. (D2500) -52 <-60 -57 -51 <-60 CFPP, .degree.
C. (D6371*) -59 -60 -60 -59 -60
[0041] Again, for the most part, Cloud Point values for the blends
appeared to be significantly reduced by the addition of the
biodiesel component with virtually no effect on the other measured
low temperature properties.
Example 3
[0042] The effect on the Cloud Point of adding relatively small
levels of biodiesel to Jet-A was investigated by adding different
concentrations (.about.10 ppm v/v, .about.20 ppm v/v, .about.30 ppm
v/v, and .about.40 ppm v/v) of the FAME mixture of Example 1 to the
saturated Jet A sample of Example 1. The results are shown in Table
3 below.
TABLE-US-00003 TABLE 3 Blend. No. 12 13 14 15 FAME, ppm v/v 10 20
30 40 Saturated Jet A Balance Balance Balance Balance Cloud Point,
.degree. C. -60 <-60 <-60 -59
[0043] The effect of biodiesel in lowering the Cloud Point of the
fuel/blend was notable, even at very low levels (.about.10 to
.about.50 ppm v/v) and even in the presence of significant amounts
(saturated levels) of dissolved water (.about.75 ppm v/v).
[0044] While the present invention has been described and
illustrated by reference to particular embodiments, those of
ordinary skill in the art will appreciate that the invention lends
itself to variations not necessarily illustrated herein. For this
reason, then, reference should be made solely to the appended
claims for purposes of determining the trite scope of the present
invention
* * * * *