U.S. patent application number 12/172820 was filed with the patent office on 2009-02-26 for production of fuels with superior low temperature properties from tall oil or fractionated fatty acids.
This patent application is currently assigned to Endicott Biiofuels II, LLC. Invention is credited to William Douglas Morgan.
Application Number | 20090049739 12/172820 |
Document ID | / |
Family ID | 40380845 |
Filed Date | 2009-02-26 |
United States Patent
Application |
20090049739 |
Kind Code |
A1 |
Morgan; William Douglas |
February 26, 2009 |
Production of Fuels with Superior Low Temperature Properties from
Tall Oil or Fractionated Fatty Acids
Abstract
The present invention relates to a process for the production of
fuels with superior low temperature properties. Specifically, the
present invention relates to the production of fuels that meet ASTM
and military jet fuel kerosene specifications by heterogeneous,
reactive distillation esterification of oils. The oils may be
naturally high in unsaturation, such as whole plant oils, tall oil
fatty acids, and rosin acids, or the oils may be from the
unsaturated fraction isolated from less unsaturated seed oils such
as palm olein, caprylic and caproic acids, or from mixtures
thereof.
Inventors: |
Morgan; William Douglas;
(Richmond, CA) |
Correspondence
Address: |
KING & SPALDING, LLP
1100 LOUISIANA ST., STE. 4000, ATTN.: IP Docketing
HOUSTON
TX
77002-5213
US
|
Assignee: |
Endicott Biiofuels II, LLC
Houston
TX
|
Family ID: |
40380845 |
Appl. No.: |
12/172820 |
Filed: |
July 14, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60962673 |
Jul 31, 2007 |
|
|
|
Current U.S.
Class: |
44/308 |
Current CPC
Class: |
Y02P 30/20 20151101;
C10G 2300/1011 20130101; C10L 1/02 20130101 |
Class at
Publication: |
44/308 |
International
Class: |
C10L 1/18 20060101
C10L001/18 |
Claims
1. A process for the production of fuel comprising: i) obtaining a
feedstock for the process; ii) performing a pre-esterification
step; and iii) performing an esterification step to yield a fuel
product, wherein the fuel product meets at least one ASTM or
military jet fuel kerosene specification.
2. The process according to claim 1, wherein the fuel product meets
ASTM or military jet fuel kerosene specification for freezing
point.
3. The process according to claim 1, wherein the feedstock is tall
oil fatty acids, and the pre-esterification step is the removal of
any tall oil rosin acids in excess of 4.5% from the feedstock.
4. The process according to claim 1, wherein the feedstock is whole
vegetable oil, and the pre-esterification step is the removal of a
C16 fraction.
5. The process according to claim 1, wherein the esterification
step includes esterification with an alcohol selected from
multi-functional polyols, glycols, iso-butanol, and
tert-butanol.
6. The process according to claim 1, wherein the feedstock is palm,
palm kernel, or coconut oil, and the pre-esterification step
includes hydrolysis of the feedstock and fractional distillation to
obtain a caprylic and/or caproic acid-enriched concentrate.
7. The process according to claim 1, wherein the esterification
step is heterogeneous reactive distillation esterification.
8. The process according to claim 7, wherein the esterification
occurs via a gas sparged, slurry form of heterogeneous reactive
distillation in a reaction chamber.
9. The process according to claim 1, further comprising a step of
blending the product of esterification with less than about 20% of
regular specification jet fuel such that the blended fuel product
meets at least two ASTM or military jet fuel kerosene
specifications.
10. The process according to claim 1, wherein the process is
performed on an industrial scale.
Description
[0001] This application claims priority under 35 U.S.C. 119(e) to
U.S. provisional application 60/962,673, filed Jul. 31, 2007, the
contents of which are incorporated by reference in their
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a process for the
production of fuels with superior low temperature properties.
Specifically, the present invention relates to the production of
fuels that meet ASTM and military jet fuel kerosene specifications
by heterogeneous, reactive distillation esterification of oils. The
oils may be naturally high in unsaturation, such as whole plant
oils, tall oil fatty acids, and rosin acids, or the oils may be
from the unsaturated fraction isolated from less unsaturated seed
oils such as palm olein, caprylic and caproic acids, or from
mixtures thereof.
BACKGROUND
[0003] Interest in the production of fuels acceptable for use in
airborne gas turbine engines from animal and vegetable fats has
increased due to the possibility of global warming. Unlike
petroleum-based fuels, fuels made from by-product animal fat and
vegetable oils are both renewable and carbon dioxide neutral.
However, a barrier to entry to the jet fuel market for fuels
derived from animal fat and vegetable oil is the poor low
temperature fluidity of the most popular derivatives such as
biodiesel or alkyl esters of fatty acids.
[0004] One method that has been proposed for avoiding the low
temperature failings of biodiesel esters is to co-feed raw animal
fat and vegetable oils along with diesel to a distillate
hydrotreater making Ultra-Low Sulfur Diesel (ULSD) (see e.g.,
Marker et al., "Opportunities for Biorenewables in Petroleum
Refineries," American Chemical Society Symposium, National Meeting
in Washington, D.C., Aug. 28-Sep. 1, 2005). However, this method
presents several drawbacks that have made this practice unsuitable
in practice. The process conditions for hydrotreating units for
ultra-low sulfur diesel production favor hydrodeoxygenation (HDO),
producing water that may adversely affect catalyst performance.
Likewise, HDO increases hydrogen requirements. It has also been
found that the heat released from these materials would
substantially lower catalyst cycle lengths such that several days
per year of production of both green and regular diesel would be
lost. The high acidity of the lower cost feeds (from 2 to 200 total
acid number) is well in excess of the accepted 0.5 to 0.6 TAN limit
for which standard feed-section metallurgy, typically carbon steel,
can be used. The cost of upgrading the unit just to run a small
amount of animal or vegetable fat becomes an economic disincentive.
Finally, it has been found that just 5% co-feeding could lead to a
cloud point increase of 10-15.degree. F. A diesel isomerization
catalyst would be required to counteract the cloud point increase
and preserve the green diesel molecules in the diesel pool.
Unfortunately, such isomerization catalysts are typically noble
metal catalysts and would require a two-stage hydroprocessing
scheme, which is not typical for distillate hydrotreating units,
necessitating major unit modifications.
[0005] Previous research looked at stand-alone
decarboxylation/hydrodeoxygenation as an option. Decarboxylation is
favored at lower pressures while hydrodeoxygenation increases with
increasing pressure. Decarboxylation results in odd number paraffin
production and CO.sub.2 formation whereas hydrodeoxygenation
results in even carbon number paraffin production; therefore, the
ratio of nC17 to nC18 is a measure of the DeCO.sub.2/HDO ratio.
Standard hydrotreating catalysts of NiMo, CoMo and Pd all showed
activity for both reactions. The main drawback to decarboxylation
as demonstrated by Marker et al. is a much lower yield of diesel
material due to the loss of a carbon to CO.sub.2. Again, a
disadvantage of hydrodeoxygenation is that it produces two moles of
water for every diesel-like molecule produced. Furthermore, it has
been shown from product distributions high in saturated C16, C17,
and C18 that the product would have excessively high cloud
points.
[0006] Another option that has been considered is specific
decarboxylation followed by reforming. However, this process not
only sacrifices a carbon to CO.sub.2, but also suffers from
excessive cracking of C17 material to lower hydrocarbons as a
result of the use of reforming technology for the final step.
[0007] Another option that has been considered is
hydrodeoxygenation of the methyl esters of the fatty acids from
animal fat and vegetable oils. Senol et al. (2005) studied the
reactions of methyl heptanoate and methyl hexanoate over commercial
NiMo/g-Al2O3 and CoMo/g-Al2O3 hydrotreating catalysts in either
oxide or sulphide form. The work involved hydrocracking to a
substantial amount of gasoline range material such as hexenes and
heptenes.
[0008] In order to overcome the limitations of the of the prior art
for the production of bioderived jet fuel, it is an object of this
invention to provide a means of producing jet fuel grade material
from plant and animal oils.
SUMMARY
[0009] In one embodiment, whole plant oils naturally high in
unsaturated fatty and rosin acids such as tall oil fatty acids and
rosin acids isolated from pine trees during the Kraft pulping
process are esterified. Whole plant oils such as tall oil and its
derivatives represent a source of highly unsaturated oils with
excellent low temperature properties that are further enhanced via
esterification with alcohols.
[0010] In another embodiment of the current invention, an
unsaturated fraction is isolated from a less saturated oil and then
esterified. For example, palm oil is regularly separated into and
highly saturated (stearin) and unsaturated (olein) fractions via
fractional crystallization. The olein fraction represents an
excellent feedstock for producing jet fuel esters. The same
separation technique can be applied to other vegetable or animal
oils such that a highly unsaturated fraction is isolated and
esterified. In one embodiment, the low temperature properties of
some whole plant and seed oils such as tall oil fatty acids and
rosins can be improved by separation of the C18 and C16 fractions
by distillation. This is possible because the C16 fraction is
normally saturated while the C18 fraction is highly
unsaturated.
[0011] It is another embodiment of the invention to esterify
caprylic (C8) and caproic (C6) fatty acids. Palm and coconut oils
as well as cow butter are rich in these carboxylic acids. Obtaining
these carboxylic acids in pure form may involve first hydrolyzing
the whole oil to yield glycerin and fatty acids, and then
fractionating the fatty acids by distillation to yield a caprylic
and caproic fatty acid concentrate.
[0012] It is a further embodiment of the invention to avoid low
temperature problems caused by contamination associated with other
wet chemical methods used to produce fuel esters. For example,
transesterification reactions catalyzed with bases such as NaOH and
esterification reactions catalyzed with acids such as sulfuric acid
tend to leave behind a certain amount of soap contamination in the
fuel. This soap readily forms solid particles at temperatures well
in excess of jet fuel freezing points making these processes
unsuitable for use even with tall oil derivatives.
[0013] While it is possible to "winterize" or "fractionally
crystallize" esters produced from a variety of feedstocks using a
variety of wet chemical transesterification or esterification
processes such that the low freeze point fraction is suitable for
use as jet fuel, such processes not only increase capital costs and
complexity substantially, but also suffer from yield loss.
[0014] Thus, high yields of fuels that are equivalent or otherwise
superior to petroleum-derived jet fuel can be produced with
acceptable capital cost by starting with suitably unsaturated fatty
acids such as tall oil acids, by fractionally crystallizing whole
oils, by distilling out C16 fractions, by recovering a
caprylic/caproic acid concentrate, or by a mixture of the above,
and utilizing the esterification process of the current invention
to thereby avoid soap or glycerin contamination of the product.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 demonstrates the sequence of operations according to
one embodiment of the invention as applied to whole plant oils such
as tall oil fatty acid and rosin.
[0016] FIG. 2 demonstrates the sequence of operations according to
another embodiment of the invention where tall oil is first
distilled to remove the C16 fraction.
[0017] FIG. 3 demonstrates the sequence of operations according to
another embodiment of the invention where glyceride-containing feed
is first split and then distilled to remove the C16 fraction and
concentrate the unsaturated C18 fraction molecules.
[0018] FIG. 4 demonstrates the sequence of operations according to
another embodiment of the invention where caprylic and caproic
acids are purified from palm or coconut oil prior to
esterification.
DETAILED DESCRIPTION
[0019] The present invention provides a method of producing
bio-derived fuel that meets jet fuel kerosene standards. Jet fuel
standards are set by standards organizations, pipelines, and
various militaries. In general, the key specification that
separates jet fuel kerosene from regular kerosene and diesel is
freeze point. For the most part, the esters of plant and animal
oils fail freeze point tests by a large margin. According to the
invention, certain whole plant oils and especially tall oil fatty
acids and rosin acids, the unsaturated fraction of seed oils, and
caprylic and caproic acid represent exceptions to this rule.
Furthermore, according to the invention, utilizing heterogeneous
reactive distillation instead of wet chemical methods of
esterification produces reduces contamination of the fuel with
higher melting substances such as soap and glycerin. Therefore, one
object of this invention is to employ heterogeneous reactive
distillation to esterify suitably unsaturated whole plant oils,
especially tall oil acids and rosins, the unsaturated fraction of
other plant and animal oils, and/or caprylic and caproic acid to
produce specification jet fuel.
[0020] There are numerous specifications for jet fuel issued by
standards organizations, pipelines, government entities, and
militaries. A summary of these has been published by ExxonMobil
(ExxonMobil, World Jet Fuel Specifications With Avgas Supplement,
2005, incorporated herein by reference). The most difficult
specification to meet when attempting to apply bio-fuel technology
is freeze point. Freeze point is similar to the Cloud Point and
Cold Flow Plugging point specifications used in biodiesel
specifications. To measure freeze point, ones takes a sample of
fluid down in temperature past the point at which crystals form and
then slowly warms the fluid back up until all crystals disappear.
The temperature at which all crystals disappear is the freeze
point.
[0021] Other specifications may be met or exceeded by the products
of this invention except for viscosity, density, energy content,
and distillation range, depending on the particular embodiments
employed. Unlike freeze point, however, these specifications can be
reached by blending in relatively small amounts of regular
specification jet fuel. By small amounts is meant less than about
20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%,
6%, 5%, 4%, 3%, 2%, or 1% of regular specification jet fuel. Freeze
point is little affected by blending because given time, crystals
will form, while the specification is not for the temperature at
which the crystals form, but that at which they melt. Therefore,
the crystals that form from regular jet fuel in a jet fuel/bio-fuel
blend may act as nucleation points for the biofuel crystals. Upon
heating, the biofuel part of the crystals may then persist to
higher temperatures.
[0022] As an example, an ester product made from tall oil fatty
acids will exceed maximum boiling point, density, and viscosity.
While it will also have lower heat content than specification jet
fuel, a 10% tall oil ester blend with jet fuel will meet all
specifications. On the other hand, caprylic and caproic acids have
the advantage of meeting all specifications except energy content.
Because they pass more tests, higher concentration blends are
possible with caprylic and caproic acids.
[0023] It is an embodiment of the invention to provide a method for
obtaining an alkyl esters based biofuel which forms crystals that
melt at lower temperatures than most alkyl ester biofuels. In one
embodiment, the invention encompasses five additional methods that
together or alone lead to fuels with superior low temperature
properties.
[0024] The first method utilizes tall oil fatty acids that may or
may not be contaminated with tall oil rosin acids as the feedstock
to the esterification method of the invention. Tall oil
rosin-contaminated tall oil fatty acids are not only less expensive
but they also produce bio-jet fuel that has a lower freeze point up
to a certain level of contamination. This can be seen in Table 1,
where increasing rosin content leads to lower titers up to a level
between 1.8 and 4.5%. Titer is another word for a measure of
crystallization temperature but not necessarily freeze point.
However, the analogy is consistent. By starting with these
materials, and esterifying them according to the invention using
various alcohols, one can prepare esters that have exceptionally
low freeze point.
TABLE-US-00001 TABLE 1 Typical Properties Fatty Acids Product Fatty
Rosin Color, Acid Iodine Titer, Family Acids, % Acids, %
Unsaponifiables, % Gardner Number Number .degree. C. Tall Oil 97.5
0.8 1.7 2+ 194 128 9 Fatty Acids 96.5 1.5 2.0 3+ 193 135 0 96.0 1.8
2.2 4 192 135 -7 92.0 4.5 3.5 6 191 131 -5 91.0 0.5 8.5 5 180 120 6
Distilled 86 11.5 2.5 8 191 -- 3 Tall Oils 63 29 8 8 182 -- 2 70 28
2 7 187 -- 11 49 48 3 7+ 174 -- -- Tall Oil 76 2.5 21.5 -- 165 --
45 Light Ends Tall Oil 51 28 -- -- 145 -- -- Pitch 3 31 -- -- 68 --
-- indicates data missing or illegible when filed
[0025] The second method involves removing the C16 fraction from
various whole oils via distillation such as those derived from tall
oil, palm, soybean, canola, and rapeseed in order to leave behind
the a higher concentration of the highly unsaturated C18:1, C18:2,
and C18:3's. This method is suited to tall oils which may be
manufactured by distillation such that removing the C16 fraction
may involve a modification of existing distillation conditions.
Fractional distillation may also be used for the ester product
itself.
[0026] The third method involves the choice of alcohol used to
esterify the fatty acids (and rosin acids in the case of tall oils)
according to the method of the invention. Multi-functional polyols,
glycols, iso-butanol, and tert-butanol can each produce bio-jet
esters with exceptionally low freeze points as well as higher
energy contents than methyl, ethyl, and propyl esters.
[0027] The fourth method of the invention involves esterification
of a caprylic (C8) and/or caproic (C6) acid concentrate. In one
embodiment, obtaining the concentrate begins with hydrolysis of
whole palm, palm kernel, or coconut oil. The free fatty acids that
result are then fractionated by distillation to yield a distillate
rich in caprylic and caproic acid. As can be seen from Table 2
(adapted from Graboski, M. S. et al., "Combustion of Fat and
Vegetable Oil Derived Fuels in Diesel Engines," Prog. Energy
Combust. Sci., Vol. 24, pp. 125-164, 1998), the esters of caprylic
and caproic acid have excellent freeze points.
TABLE-US-00002 TABLE 2 Fatty acids Methyl esters Melting Boiling
Melting Boiling Acid No. of point point point point chain carbons
Structure (.degree. C.) (.degree. C.) (.degree. C.) (.degree. C.)
Caprylic 8 CH.sub.3(CH.sub.2).sub.6COOH 16.5 239 -40 193 Capric 10
CH.sub.3(CH.sub.2).sub.8COOH 31.3 269 -18 224 Lauric 12
CH.sub.3(CH.sub.2).sub.10COOH 43.6 304 5.2 262 Myristic 14
CH.sub.3(CH.sub.2).sub.12COOH 58.0 332 19 295 Palmitic 16
CH.sub.3(CH.sub.2).sub.14COOH 62.9 349 30 338 Palmitoleic 16
CH.sub.3(CH.sub.2).sub.5CH.dbd.CH(CH.sub.2).sub.7COOH 33 -- 0 --
Stearic 18 CH.sub.3(CH.sub.2).sub.16COOH 69.9 371 39.1 352 Oleic 18
CH.sub.3(CH.sub.2).sub.7CH.dbd.CH(CH.sub.2).sub.7COOH 16.3 -- -19.9
349 Linoleic 18
CH.sub.3(CH.sub.2).sub.4CH.dbd.CHCH.sub.2CH.dbd.CH(CH.sub.2).sub.7COOH
-5 -- -35 366 Linolenic 18
CH.sub.3CH.sub.2CH.dbd.CHCH.sub.2CH.dbd.CHCH.sub.2CH.dbd.CH(CH.sub.2).sub-
.7COOH -11 -- -- -- Arachidic 20 CH.sub.3(CH.sub.2).sub.18COOH 75.2
-- 50 -- Eicosenoic 20
CH.sub.3(CH.sub.2).sub.7CH.dbd.CH(CH.sub.2).sub.9COOH 23 -- -15 --
Behenic 22 CH.sub.3(CH.sub.2).sub.20COOH 80 -- 54 -- Erucic 22
CH.sub.3(CH.sub.3).sub.7CH.dbd.CH(CH.sub.2).sub.11COOH 34 -- --
--
These esters also have lower densities and viscosities than the
esters of tall oil meaning that they can be blended into jet fuel
at a higher percentage without the blend going out of
specification.
[0028] The fifth method according to the invention, which in
combination with the use of highly unsaturated fatty acids as feed
stocks leads to fuels with superior low temperature properties,
includes a method of reactive distillation (such as disclosed in
U.S. Pat. No. 5,536,856, incorporated herein by reference). The
method according to the invention involves both the application of
reactive distillation and slurry reactor technology. The
esterification method itself is superior to other wet chemical
methods because it does not lead to soap formation. Soap
contamination always leads to poor freeze points. In one
embodiment, the esterification method is particularly applicable to
tall oil fatty acids and rosin and caprylic and caproic acids
because these materials may be recovered in their fatty acid state.
The glycerides in other starting materials must be "split" to a
relatively high degree (for example, to about 90% or greater) prior
to esterification in order to obtain optimum catalyst life.
[0029] Referring to FIG. 1, tall oil fatty acid, or other whole
plant oils, that may contain some amount of tall oil or other rosin
acids, is esterified by a reactive distillation, slurry reactor
method of the invention. This method is described in detail in U.S.
Pat. No. 5,536,856 incorporated herein by reference.
[0030] Referring to FIG. 2, tall oil fatty acid is manufactured
such that the C16 fraction is separated from the C18 fraction of
whole plant, seed, and animal oils during distillation. The C18
fraction is then esterified according to the esterification method
of the invention.
[0031] Referring to FIG. 3, the glycerides in less suitably
unsaturated whole plant, seed, and animal oils, especially rapeseed
and canola, are first split into fatty acids and glycerin either by
hydrolysis or saponification. The C16 fraction is then distilled
from the resulting fatty acids prior to esterification of the C18
fraction.
[0032] Referring to FIG. 4, palm or coconut oil is first subjected
to hydrolysis. The resulting free fatty acids are then fractionated
in order to obtain a caprylic/caproic concentrate. The concentrate
may contain minor amounts of C10, C12, C14, C16, and C18. However,
the lower the contamination with these higher carboxylic acids, the
better the low temperature performance of the fuel. The
caprylic/caproic concentrate is then subjected to esterification
according to the esterification method of the invention.
[0033] In each of the methods, the choice of alcohol will affect
the freeze point of the resulting bio-jet fuel esters. For example,
tert-butanol produces esters with a much lower freeze point for the
same feedstock than methanol. The use of all C1 to C8 alcohols,
polyols, glycols, and glycol ethers can be envisioned according to
the invention. U.S. Pat. No. 5,536,856, incorporated herein by
reference, teaches different configurations depending on the
boiling point of the alcohol.
[0034] In one embodiment, the process is performed on an industrial
scale. For example, in a preferred embodiment, production occurs
from 500 kg or more of feedstock per day. Alternatively, production
may occur on batches of 1,000 kg, 5,000 kg, 10,000 kg or more
feedstock per day. Global jet fuel and kerosene production is
estimated at several million tons per year.
[0035] It will be understood by those skilled in the art that the
drawings are diagrammatic and that further items of equipment such
as reflux drums, pumps, vacuum pumps, temperature sensors, pressure
sensors, pressure relief valves, control valves, flow controllers,
level controllers, holding tanks, storage tanks, and the like may
be required in a commercial plant. The provision of such ancillary
items of equipment forms no part of the present invention and is in
accordance with conventional chemical engineering practice.
[0036] Modifications and variations of the present invention
relating to a the selection of reactors, feedstocks, alcohols and
catalysts will be obvious to those skilled in the art from the
foregoing detailed description of the invention. Such modifications
and variations are intended to come within the scope of the
appended claims. All numerical values are understood to be prefaced
by the term "about" where appropriate. All references cited herein
are hereby incorporated by reference in their entirety.
* * * * *