U.S. patent application number 13/849693 was filed with the patent office on 2013-09-26 for bacterial production of jet fuel and gasoline range hydrocarbons.
The applicant listed for this patent is David Bradin. Invention is credited to David Bradin.
Application Number | 20130247452 13/849693 |
Document ID | / |
Family ID | 49210459 |
Filed Date | 2013-09-26 |
United States Patent
Application |
20130247452 |
Kind Code |
A1 |
Bradin; David |
September 26, 2013 |
Bacterial Production of Jet Fuel and Gasoline Range
Hydrocarbons
Abstract
Methods for forming hydrocarbon products from bacteria, namely,
bacteria which produce fatty acids, are disclosed. The methods
involve the bacterial production of fatty acids, the thermal
decarboxylation of the resulting fatty acids, the hydrocracking and
isomerization of the decarboxylation product, and the distillation
to yield the desired hydrocarbon fractions. The products can be
isolated in the gasoline, jet and/or diesel fuel ranges. Thus,
bacteria can be used to produce products in the gasoline, jet
and/or diesel fuel ranges which are virtually indistinguishable
from those derived from their petroleum-based analogs.
Inventors: |
Bradin; David; (Chapel Hill,
NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bradin; David |
Chapel Hill |
NC |
US |
|
|
Family ID: |
49210459 |
Appl. No.: |
13/849693 |
Filed: |
March 25, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61614714 |
Mar 23, 2012 |
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Current U.S.
Class: |
44/388 ;
435/166 |
Current CPC
Class: |
C10G 2300/1011 20130101;
C10G 2400/02 20130101; C10G 3/40 20130101; C10G 65/12 20130101;
C10G 2400/04 20130101; C10G 47/00 20130101; C10G 3/50 20130101;
C10G 2400/08 20130101; Y02P 30/20 20151101 |
Class at
Publication: |
44/388 ;
435/166 |
International
Class: |
C10G 3/00 20060101
C10G003/00 |
Claims
1. A method of forming a hydrocarbon product, comprising the steps
of: a) cultivating bacteria which produce a fatty acid product, to
provide a source of fatty acids, b) isolating the fatty acids, c)
performing thermal decarboxylation on the fatty acids to form a
thermal decarboxylation product stream, d) hydrocracking the
thermal decarboxylation product stream, and c) isolating a product
in the gasoline, jet, or diesel fuel range.
2. The method of claim 1, wherein the product is in the jet
range.
3. The method of claim 1, wherein all or a portion of the product
is subjected to isomerization conditions.
4. The method of claim 1, wherein all or a portion of the product
is subjected to hydrogenation, hydrotreatment, and/or
hydrofinishing conditions.
5. The method of claim 3, wherein the product is in the jet
range.
6. The method of claim 4, wherein all or a portion of the product
is subjected to isomerization conditions.
7. The method of claim 3, wherein all or a portion of the product
is subjected to hydrogenation, hydrotreatment, and/or
hydrofinishing conditions.
8. The method of claim 1, wherein the product is in the diesel or
gasoline range.
9. The method of claim 8, wherein all or a portion of the product
is subjected to hydrogenation, hydrotreatment, and/or
hydrofinishing conditions.
10. The method of claim 8, wherein all or a portion of the product
is subjected to isomerization conditions.
11. A jet fuel or jet fuel additive produced by the method of claim
5.
12. A jet fuel or jet fuel additive produced by the method of claim
7.
13. The jet fuel or jet fuel additive of claim 11, further
comprising petroleum-based jet fuel.
14. A method of forming a renewable jet fuel or jet fuel additive,
comprising the steps of: a) cultivating a bacteria which produces
fatty acids, b) isolating the fatty acids, c) performing thermal
decarboxylation on the fatty acids to form a thermal
decarboxylation product stream, d) hydrocracking the thermal
decarboxylation product stream, e) subjecting the hydrocracked
product stream to isomerization conditions, and f) isolating a
product in the jet fuel range.
15. A method of forming a renewable diesel fuel or diesel fuel
additive, comprising the steps of: a) cultivating a bacteria which
produces fatty acids, b) isolating the fatty acids, c) performing
thermal decarboxylation on the fatty acids to form a thermal
decarboxylation product stream, optionally, d) hydrotreating the
product stream resulting from the thermal decarboxylation step, and
e) isolating a product in the diesel fuel range.
Description
[0001] This application claims priority from U.S. provisional
application No. 61/614,714 filed on Mar. 23, 2012 and is
incorporated herein in its entirety by reference.
FIELD OF THE INVENTION
[0002] The invention is generally in the area of bacterial
production of fatty acids, and conversion of the fatty acids to
hydrocarbons in the jet, diesel, or gasoline ranges.
BACKGROUND OF THE INVENTION
[0003] There is currently a strong interest in alternative fuels.
These fuels predominantly come from two feedstocks, vegetable oils
and sugars. Biodiesel is formed from vegetable oil, and ethanol
comes from sugar.
[0004] Vegetable oils are mostly comprised of triglycerides, esters
of glycerol, and three fatty acids. Fatty acids are, in turn,
aliphatic compounds containing 4 to 24 carbon atoms, ideally
between 10 and 18 carbon atoms, and having a terminal carboxyl
group. Diglycerides are esters of glycerol and two fatty acids, and
monoglycerides are esters of glycerol and one fatty acid. Naturally
occurring fatty acids, with only minor exceptions, have an even
number of carbon atoms and, if any unsaturation is present, the
first double bond is generally located between the ninth and tenth
carbon atoms. The characteristics of the triglyceride are
influenced by the nature of their fatty acid residues.
[0005] Biodiesel fuels are fatty acid ethyl and/or methyl esters.
These esters are typically prepared by transesterifying
triglycerides, the major component in fats and oils, with ethanol
and/or methanol, in the presence of an acid or base catalyst.
Biodiesel fuels are associated with some limitations. For example,
some research indicates that they cause higher emissions of
nitrogen oxides (NO.sub.x), increased wear on engine components,
and fuel injector coking ("Progress in Diesel Fuel from Crop Oils,"
AgBiotechnology, (1988)). Also, biodiesel fuel does not provide as
much power as petroleum-based diesel is burned (See, for example,
Jori, et al., Hungarian Agricultural Engineering, 6:7, 27-28
(1993)), and the diesel engines may need to be retuned in order to
run efficiently on biodiesel.
[0006] Another effort at producing a renewable fuel has involved
the thermal conversion of animal carcasses to a liquid oil product
and a water-soluble inorganic product. When animal carcasses are
heated, at around 250 C, the triglycerides hydrolyze into glycerol
and free fatty acids, and at around 500 C, the free fatty acids
decarboxylate to form a mixture of products that relate to the
hydrocarbon chains in the original fatty acids. This process is
known as thermal decarboxylation. The rate of this process can be
accelerated by the addition of various catalysts, though the end
game is still the same--removal of a carboxylic acid moiety from
the end of the fatty acid.
[0007] Most automobiles run on gasoline, and airplanes run on jet
fuel, not diesel. It would be advantageous to provide a method for
forming alternative fuel sources from vegetable oil feedstocks that
have tunable molecular weights and octane or cetane ratings, so
that a variety of gasoline, jet fuel, or diesel fuel compositions
can be prepared as desired. The present invention provides such
methods, as well as renewable gasoline, jet fuel, and diesel fuel
compositions.
[0008] Allowed U.S. Publication No. 20080229654 to Bradin discloses
a process for converting fatty acids or triglycerides to gasoline,
jet, or diesel fuel, and provides a list of animal and vegetable
sources for the triglycerides. U.S. Pat. No. 7,816,570 to Roberts
et al. also discloses a process for converting triglycerides to jet
fuel. The difference between the Roberts and the Bradin process is
that the Roberts process burns the glycerol derived from the
hydrolysis of triglycerides to produce the energy to run the
overall process, whereas, in other patent applications, Bradin
discloses converting glycerol to glycerol ethers and using the
glycerol ethers as fuel additives. The contents of these references
are incorporated herein in their entirety.
[0009] The limitation associated with using triglycerides is that
the production of the raw materials is somewhat limited. Bacteria
and algae are potential feedstocks for producing fatty acid and
triglycerides, respectively, that are believed to hold great
promise. It would therefore be desirable to provide methods for
converting bacterial products to fuels. The present invention
provides such methods.
SUMMARY OF THE INVENTION
[0010] Fuel additives and fuel compositions, and methods for their
preparation and use directly as fuels, or as blends with
conventional gasoline, jet, and/or diesel fuel, are disclosed.
[0011] Fatty acids are used to prepare the fuel additives and/or
fuel compositions, and these are subjected to thermal
decarboxylation to remove the carboxylic acid group. The resulting
decarboxylated products comprise hydrocarbons in the C.sub.10-20
range, and, depending on the starting materials, include one or
more double bonds. If desired, the double bonds can be hydrotreated
to produce linear paraffins.
[0012] Gasoline predominantly includes hydrocarbons in the
molecular weight range of C.sub.5-9, for example, C.sub.6-8.
Gasoline tends to include isoparaffins, so while intermediate
C.sub.5-9-containing fractions, for example, C.sub.6-8 fractions,
can advantageously be isolated for direct use or sale, they can
also be subjected to additional processing steps, such as
isomerization and hydrotreatment.
[0013] Diesel fuel has a preferred molecular weight range of
C.sub.10-20, ideally at the lower end of this range. By selecting
appropriate thermal decarboxylation products, yields of products in
the diesel range can be maximized. As the products include
carbon-carbon double bonds, an optional hydrotreatment step may be
performed.
[0014] There are many types of jet fuel, including kerosene-type
jet fuel and wide-cut jet fuel. Kerosene-type jet fuel has a carbon
number distribution between about 8 and 16 carbon numbers; wide-cut
jet fuel, between about 5 and 15 carbon numbers. By using
appropriate distillation conditions to separate the products of the
thermal decarboxylation and hydrocracking steps, hydrocarbons in
either jet fuel range can be provided. These can be used as is, or
hydrotreated to hydrogenate the double bonds and/or isomerized to
provide isoparaffins.
[0015] The thermal decarboxylation products are subjected to
hydrocracking to provide products in a desired molecular weight
range, isomerization to provide products with a desired degree of
branching, and/or hydrotreating/hydrofinishing steps. The desired
molecular weight range and degree of branching will, of course,
depend on whether it is desired to provide a diesel, gasoline, or
jet fuel composition, or additive for including in such
compositions.
[0016] Alternative fuel compositions including the resulting
products can be prepared by blending the products with gasoline,
diesel fuel, or jet fuel, as appropriate. In one embodiment, the
resulting alternative fuel contains between approximately 25 and 98
percent petroleum-based gasoline, diesel or jet fuel and between
approximately 2 and 75 percent of the products from the molecular
averaging or post-treatment steps.
[0017] In one embodiment, once the fatty acids are decarboxylated,
they are used directly as diesel fuel, or as an additive in diesel
fuel, without further steps such as hydrocracking or isomerization.
In one aspect of this embodiment, double bonds in the
decarboxylation product are hydrogenated.
DETAILED DESCRIPTION OF THE INVENTION
[0018] This invention uses a two-stage process for producing jet
fuel, diesel fuel, and/or gasoline from food and non-food
feedstocks. First, a genetically-engineered microorganism is used
to convert the feedstock into fatty acids. This organism is ideally
produced using a computational design process to identify favorable
genetic modifications to maximize fatty acid production. Second,
fatty acids are converted into jet fuel using a chemical process.
The jet fuel can be domestically produced and can be used by the
aviation and defense industries, and the gasoline and diesel can be
used in conventional gasoline and diesel engines, as well as in
flexible fuel engines.
[0019] Fuel compositions, as well as methods for preparing the
compositions, are disclosed. The fuel composition can be used as
gasoline, jet fuel, and/or diesel fuel, or used as additives to
such fuels.
[0020] In its broadest aspect, the present invention is directed to
an integrated process for producing fuels, including jet fuel,
gasoline and diesel. The process involves the thermal
decarboxylation of fatty acids to form a thermal decarboxylation
product, which can be used as is, or subjected to further steps,
such as isomerization, hydrocracking, and hydrotreatment.
[0021] In some embodiments, the processes described herein are
integrated processes. As used herein, the term "integrated process"
refers to a process which involves a sequence of steps, some of
which may be parallel to other steps in the process, but which are
interrelated or somehow dependent upon either earlier or later
steps in the total process.
[0022] There are numerous advantages provided by the processes
described herein. The processes convert bacteria-derived fatty
acids, which tend to be outside the range of gasoline, diesel
and/or jet fuel, into products within these ranges.
[0023] The following definitions will further define the
invention:
[0024] The term "alkyl", as used herein, unless otherwise
specified, refers to a saturated straight, branched, or cyclic
hydrocarbon of C.sub.1-6, and specifically includes methyl, ethyl,
propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, cyclopentyl,
isopentyl, neopentyl, hexyl, isohexyl, cyclohexyl, 3-methylpentyl,
2,2-dimethylbutyl, and 2,3-dimethylbutyl.
[0025] The term "olefin" refers to an unsaturated straight,
branched or cyclic hydrocarbon of C.sub.2-10, and specifically
includes ethylene, propylene, butylene, isobutylene, pentene,
cyclopentene, isopentene, hexene, cyclohexene, 3-methylpentene,
2,2-dimethylbutene, 2,3-dimethylbutene, 1-heptene, 2-heptene,
3-heptene, 1-octene, 2-octene, 3-octene, 4-octene, 1-nonene,
2-nonene, 3-nonene, 4-nonene, 1-decene, 2-decene, 3-decene,
4-decene, and 5-decene. Ethylene, propylene, butylenes, and
isobutylene can be preferred due to their relatively low cost, and
C.sub.2-8 olefins, or, preferably, C.sub.2-4 olefins (low molecular
weight olefins) can be preferred. Low molecular weight olefins can
include other olefins outside the C.sub.2-4 range, but ideally, the
majority (51% or more) of the olefins in a low molecular weight
olefin feedstock are in this range. In one embodiment, the olefins
comprise substituted olefins.
I. Fuel Composition
[0026] The fuel composition prepared using the processes described
herein can include alkanes in the gasoline, jet fuel and/or diesel
fuel ranges, as desired. While thermal decarboxylation products are
present, the composition can optionally include fatty acid alkyl
esters, which can provide adequate lubrication when used in an
amount of about 2 percent by volume or more.
[0027] The hydrocarbons produced using the processes described
herein typically have average molecular weights in the C.sub.5-20
range. The molecular weight can be controlled by adjusting the
molecular weight and proportions of the decarboxylated fatty acids
(C.sub.10-20 range), and the low molecular weight olefins, that are
subjected to molecular averaging (olefin metathesis) conditions.
Fuel compositions with boiling points in the range of between about
68-450 F, more preferably between about 250-370 F, are preferred.
The currently most preferred average molecular weight is around
C.sub.8-20, which has a boiling point in the range of roughly 345
F, depending on the degree of branching. Specifications for the
most commonly used diesel fuel (No. 2) are disclosed in ASTM D 975
(See, for example, p. 34 of 1998 Chevron Products Company Diesel
Fuels Tech Review). The minimum flash point for diesel fuel is 52 C
(125 F). Specifications for jet fuel are disclosed in ASTM D 1655,
standard Specification for Aviation Turbine Fuels. The minimum
flash point for jet fuel is typically 38 C.
[0028] The process is adaptable to generate higher molecular weight
fuels, for example, those in the C.sub.15-20 range, or lower
molecular weight fuels, for example, those in the C.sub.5-8 range.
Preferably, the majority of the composition includes compounds
within about 8, and more preferably, within about 5 carbons of the
average. Another important property for the fuel is that it has a
relatively high flash point for safety reasons. Preferably, the
flash point is above 90 C, more preferably above 110 C, still more
preferably greater than 175 C, and most preferably between 175 C
and 300 C.
[0029] The fuel can also be used as a blending component with other
fuels. For example, the fuel can be used as a blending component
with fuels derived from crude oil or other sources.
II. Components used to Prepare the Fuel Composition [0030] A. Free
Fatty Acids
[0031] All or part of the free fatty acids are obtained from
bacterial sources. In addition to the fatty acids derived from
bacterial sources, a portion of the fatty acids can be derived from
the hydrolysis of triglycerides, including vegetable oils and fats,
as well as animal oils and fats. Examples of suitable vegetable
oils include, but are not limited to, crude or refined soybean,
corn, coconut (including copra), palm, rapeseed, cotton and oils.
Examples of suitable animal fats include, but are not limited to,
tallow, lard, butter, bacon grease and yellow grease.
Naturally-occurring fats and oils are the preferred source of
triglycerides because of their abundance and renewability. Oils
with a higher boiling point are preferred over oils with a lower
boiling point. Animal carcasses can be used, though this may not be
preferred due to the presence of various by-products (i.e.,
compounds other than decarboxylated fatty acids) in the thermal
decarboxylation product stream (although the by-products can be
removed, if desired). In one embodiment, all or part of the fatty
acids can come from the hydrolysis of vegetable oil.
[0032] Fatty acid biosynthesis (FAB) is necessary for the
production of bacterial cell walls, and therefore is essential for
the survival of bacteria (Magnuson et al., 1993, Microbiol. Rev.
57:522-542). The fatty acid synthase system in E. coli is the
archetypal type II fatty acid synthase system. Multiple enzymes are
involved in fatty acid biosynthesis, and genes encoding the enzymes
fabH, fabD, fabG, acpP, and fabF are clustered together on the E.
coli chromosome. Clusters of FAB genes have also been found in
Bacillus subtilis, Haemophilus influenza Rd, Vibrio harveyi, and
Rhodobacier capsulatus. Examples of FAB genes in B. subtilis
include fabD, yjaX and yhjB (encoding synthase III), fabG, ywpB,
yjbW, yjaY, ylpC, fabG, and acpA. The ylpC, fabG, and acpA genes
are contained within a single operon that is controlled by the
PylpC promoter.
[0033] Compounds that promote the production of fatty acids can be
introduced to bacteria to encourage the production of fatty
acids.
[0034] Genetically modified E. coli microorganisms, or other
bacteria, can be produced such that they overproduce fatty acids,
which are used in the instant process to make fuels. Enzymes can be
expressed which can enhance fatty acid production.
[0035] Although most bacteria produce fatty acids as cell envelope
precursors, the biosynthesis of fatty acids is tightly regulated at
multiple levels. By introducing four distinct genetic changes into
the E. coli genome, Lu et al. (Metabolic Engineering, Volume 10,
Issue 6, November 2008, Pages 333-339, Engineering Metabolic
Pathways for Biofuels Production) have engineered an efficient
producer of fatty acids. Under fed-batch, defined media
fermentation conditions, 2.5 g/L fatty acids were produced by this
metabolically engineered E. coli strain, with a specific
productivity of 0.024 g/h/g dry cell mass and a peak conversion
efficiency of 4.8% of the carbon source into fatty acid products.
At least 50% of the fatty acids produced were present in the free
acid form. The contents of the Lu et al. paper are hereby
incorporated by reference in their entirety.
[0036] Streen et al., Nature, Vol 463, 28 Jan. 2010, discloses the
production of fatty acids from the industrial microorganism E.
coli. E. coli is approximately 9.7% lipid, produces fatty acid
metabolites at the commercial productivity of 0.2 g l21 h21 per
gram of cell mass just to grow, can achieve product-dependent mass
yields of 30-35% 4, and is exceptionally amenable to genetic
manipulation. Combining this natural fatty acid synthetic ability
with new biochemical reactions realized through synthetic biology
has provided a means to divert fatty acid metabolism directly
towards fuel and chemical products of interest The product of
microbial fatty acid biosynthesis is fatty acyl-ACP (acyl carrier
protein), which can then be directed to cellular components such as
structural or storage lipids 5,6. The accumulation of fatty
acyl-ACP feedback inhibits fatty acid biosynthesis. The expression
of a cytoplasmic thioesterase was previously shown to result in
hydrolysis of these acyl-ACPs, deregulation of fatty acid
biosynthesis, and overproduction and secretion of significant
levels of free fatty acids.
[0037] By cytosolic expression of a native E. coli thioesterase
('tesA--a `leaderless` version of TesA that is targeted to the
cytosol), normally localized to the periplasm, Streen demonstrated
free fatty acid production of 0.32 g l21, similar to previous
findings (FIG. 2)6,8. 'TesA exhibits a preference for C14 fatty
acyl-ACPs, although a range of free fatty acids (C8-C18) is
observed when 'TesA is produced The length of the fatty acid chain
produced can be controlled by expressing alternative thioesterases
from plants9. To improve free fatty acid production further, we
eliminated the first two competing enzymes associated with
b-oxidation, FadD and FadE, resulting in an extra three- to
fourfold increase in titre to, 1.2 g l21. 'TesA-DfadE affected a 6%
yield of fatty acids from 2% glucose in shake flasks, 14% of the
theoretical limit. The contents of the Streen et al. paper are
hereby incorporated by reference in their entirety.
[0038] These are just a few references related to the bacterial
production of fatty acids. Efforts to date have involved
esterifying the fatty acids to produce biodiesel. The use of these
fatty acids to produce jet fuel, gasoline, or diesel (not
biodiesel) range hydrocarbons is first described herein. Using
these teachings, and other knowledge already present in the art,
one can use bacteria to produce fatty acids as a feedstock for the
process described herein.
[0039] Efforts are underway, for example, by the company LS9, to
modify bacteria so as to produce fatty acids, and then, within the
bacteria, to cleave the acid into a hydrocarbon. However, it is
unclear whether bacteria can tolerate a high concentration of
linear hydrocarbons. It is clear, and it is an object of the
present invention, that the bacteria can produce fatty acids, and
that these fatty acids can be isolated separately from the
bacteria, and then subjected to thermal decarboxylation conditions
to produce hydrocarbons, which are then subjected to further
process steps, as described herein, to produce jet fuel, gasoline,
and/or diesel range hydrocarbons, with jet fuel being particularly
preferred due to its relatively high market price. [0040] B.
Additional Components
[0041] The fuel compositions can include various additives, such as
lubricants, emulsifiers, wetting agents, densifiers, fluid-loss
additives, corrosion inhibitors, oxidation inhibitors, friction
modifiers, demulsifiers, anti-wear agents, anti-foaming agents,
detergents, rust inhibitors and the like. Other hydrocarbons, such
as those described in U.S. Pat. No. 5,096,883 and/or U.S. Pat. No.
5,189,012, can be blended with the fuel, provided that the final
blend has the necessary octane/cetane values, pour, cloud and
freeze points, kinematic viscosity, flash point, and toxicity
properties. The total amount of additives is preferably between
50-100 ppm by weight for 4-stroke engine fuel, and for 2-stroke
engine fuel, additional lubricant oil may be added.
[0042] Diesel fuel additives are used for a wide variety of
purposes; however, they can be grouped into four major categories:
engine performance, fuel stability, fuel handling, and contaminant
control additives.
[0043] Engine performance additives can be added to improve engine
performance. Cetane number improvers (diesel ignition improvers)
can be added to reduce combustion noise and smoke. 2-Ethylhexyl
nitrate (EHN) is the most widely used cetane number improver. It is
sometimes also called octyl nitrate. EHN typically is used in the
concentration range of 0.05% mass to 0.4% mass and may yield a 3 to
8 cetane number benefit. Other alkyl nitrates, ether nitrates some
nitroso compounds, and di-tertiary butyl peroxide can also be
used.
[0044] Fuel and/or crankcase lubricant can form deposits in the
nozzle area of injectors--the area exposed to high cylinder
temperatures. Injector cleanliness additives can be added to
minimize these problems. Ashless polymeric detergent additives can
be added to clean up fuel injector deposits and/or keep injectors
clean. These additives include a polar group that bonds to deposits
and deposit precursors and a non-polar group that dissolves in the
fuel. Detergent additives are typically used in the concentration
range of 50 ppm to 300 ppm. Examples of detergents and metal rust
inhibitors include the metal salts of sulfonic acids, alkylphenols,
sulfurized alkylphenols, alkyl salicylates, naphthenates and other
oil soluble mono and dicarboxylic acids such as tetrapropyl
succinic anhydride. Neutral or highly basic metal salts such as
highly basic alkaline earth metal sulfonates (especially calcium
and magnesium salts) are frequently used as such detergents. Also
useful is nonylphenol sulfide. Similar materials can be prepared by
reacting an alkylphenol with commercial sulfur dichlorides.
Suitable alkylphenol sulfides can also be prepared by reacting
alkylphenols with elemental sulfur. Also suitable as detergents are
neutral and basic salts of phenols, generally known as phenates,
wherein the phenol is generally an alkyl substituted phenolic
group, where the substituent is an aliphatic hydrocarbon group
having about 4 to 400 carbon atoms.
[0045] Lubricity additives can also be added. Lubricity additives
are typically fatty acids and/or fatty esters. Examples of suitable
lubricants include polyol esters of C.sub.12-28 acids. The fatty
acids are typically used in the concentration range of 10 ppm to 50
ppm, and the esters are typically used in the range of 50 ppm to
250 ppm.
[0046] Some organometallic compounds, for example, barium
organometallics, act as combustion catalysts, and can be used as
smoke suppressants. Adding these compounds to fuel can reduce the
black smoke emissions that result from incomplete combustion. Smoke
suppressants based on other metals, e.g., iron, cerium, or
platinum, can also be used.
[0047] Anti-foaming additives such as organosilicone compounds can
be used, typically at concentrations of 10 ppm or less. Examples of
anti-foaming agents include polysiloxanes such as silicone oil and
polydimethyl siloxane; acrylate polymers are also suitable.
[0048] Low molecular weight alcohols or glycols can be added to
diesel fuel to prevent ice formation. Additional additives can
lower a diesel fuel's pour point (gel point) or cloud point, or
improve its cold flow properties.
[0049] Drag reducing additives can also be added to increase the
volume of the product that can be delivered. Drag reducing
additives are typically used in concentrations below 15 ppm.
[0050] Antioxidants can be added to the distillate fuel to
neutralize or minimize degradation chemistry, typically in the
concentration range of 10 ppm to 80 ppm. Examples of antioxidants
include those described in U.S. Pat. No. 5,200,101.
[0051] Acid-base reactions are another mode of fuel instability.
Stabilizers such as strongly basic amines can be added, typically
in the concentration range of 50 ppm to 150 ppm, to counteract
these effects.
[0052] Metal deactivators can be used to tie up (chelate) various
metal impurities, neutralizing their catalytic effects on fuel
performance. They are typically used in the concentration range of
1 ppm to 15 ppm.
[0053] Multi-component fuel stabilizer packages may contain a
dispersant. Dispersants are typically used in the concentration
range of 15 ppm to 100 ppm.
[0054] Biocides can be used when contamination by microorganisms
reaches problem levels, typically used in the concentration range
of 200 ppm to 600 ppm.
[0055] Demulsifiers are surfactants that break up emulsions and
allow fuel and water phases to separate, and are typically are used
in the range of 5 ppm to 30 ppm.
[0056] Dispersants are well known in the lubricating oil field.
[0057] Corrosion and oxidation inhibitors are compounds that attach
to metal surfaces and form a barrier that prevents attack by
corrosive agents, and are typically are used in the range of 5 ppm
to 15 ppm.
[0058] Friction modifiers, such as fatty acid esters and amides,
glycerol esters of dimerized fatty acids, and succinate esters or
metal salts thereof, can be used.
[0059] Pour point depressants such as C.sub.8-18 dialkyl fumarate
vinyl acetate copolymers, polymethacrylates and wax naphthalene,
can be used.
[0060] Examples of anti-wear agents include zinc
dialkyldithiophosphate, zinc diary diphosphate, and sulfurized
isobutylene. Additional additives are described in U.S. Pat. No.
5,898,023 to Francisco, et al.
III. Alternative Fuel Composition
[0061] The fuels prepared as described herein can be used directly,
or combined with conventional fuels to form an alternative fuel
composition. When formulated as gasoline, diesel or jet fuels, the
compositions can be combined with gasoline, diesel and/or jet
fuels, as appropriate, or used as is, to run gasoline, diesel
and/or jet engines. The blended ratios with petroleum-based fuels
are typically such that the resulting blended fuel composition
ideally contain between about 25 to about 98 percent of the
conventional fuel and between about 2 to about 75 percent of the
compositions described herein. The components can be mixed in any
suitable manner.
IV. Methods for Preparing the Fuel Composition
[0062] A. Hydrolysis
[0063] If one starts with fatty acids derived from bacterial
sources, there is no need to perform a hydrolysis step. However, if
all or a portion of the fatty acids is derived from triglycerides,
the first step in the process involves either hydrolysis or
saponification of the triglyceride to form free fatty acids and
glycerol. Conditions for hydrolyzing/saponifying triglycerides are
well known to those of skill in the art. Although triglycerides can
be hydrolyzed during the thermal decarboxylation step, they can
also be hydrolyzed beforehand. Any acid catalyst that is suitable
for performing triglyceride hydrolysis can be used, in any
effective amount and any effective concentration. Examples of
suitable acids include, but are not limited to, hydrochloric acid,
hydrobromic acid, sulfuric acid, nitric acid, and solid catalysts
such as Dowex 50.TM..
[0064] The presence of glycerol and water in the subsequent thermal
decarboxylation step is not deleterious, although to increase
throughput, it may be desirable to remove the glycerol/water
fraction before thermal decarboxylation.
[0065] In one aspect, the hydrolysis occurs in a batch-type
process, where water, triglycerides and an acid catalyst are heated
until the hydrolysis is complete. The resulting aqueous phase
includes glycerol, water, and, if the acid catalyst is water
soluble, an acid. In another aspect, the triglycerides are
thermally hydrolyzed by heating them with water at a temperature at
or near, and, ideally, above, the boiling point of water. High
pressure steam (steam hotter than the boiling point of water) can
quickly hydrolyze triglycerides to glycerol and free fatty acids.
[0066] B. Thermal Decarboxylation/Deoxygenation of Free Fatty
Acids
[0067] Free fatty acids are converted to alkanes via thermal
decarboxylation and/or thermal decarbonylation. In one aspect, the
thermal decarboxylation of fatty acids is performed in the same
step in which a triglyceride is hydrolyzed to form glycerol/water
and free fatty acids.
[0068] In a batch or continuous process, free fatty acids,
optionally in water or an organic solvent, and optionally in the
presence of a catalyst, are subjected to thermal decarboxylation
conditions. Typically, this involves heating the free fatty acids
to a temperature of between 400-600 C, though this temperature can
be lowered by appropriate selection of catalyst.
[0069] By-products, including primarily carbon dioxide and
hydrogen, can be separately collected. The hydrogen and carbon
dioxide can be collected, with the hydrogen ideally being separated
from the carbon dioxide. The hydrogen can be used for
hydrocracking, for hydrofinishing, and/or other processing
steps.
[0070] In another aspect, the thermal decarboxylation of the fatty
acids is performed using a static mixer or other suitable means for
mixing high pressure steam and triglycerides. The high pressure
steam and triglycerides initially form the glycerol/water stream,
and the fatty acids then form the decarboxylation products,
including carbon dioxide and hydrogen. Using a static mixer or
similar apparatus, the hydrogen and carbon dioxide gases thus
formed can flow in the direction of the other products. Since the
other products tend to liquefy at higher temperatures than the
hydrogen and carbon dioxide, use of a static mixer can both
facilitate collection of the gases and minimize pressure and
foaming in the reactor, as might otherwise occur in a batch process
in which water and fatty acids are heated above the boiling points
of either. The decarboxylation reaction can occur in a time frame
suitable for using a static mixer or other suitable mixing
apparatus in a continuous process, and the shorter contact times
can minimize product degradation, as has been reported in cases
where whole animal carcasses have been subjected to these types of
elevated temperatures and pressures.
[0071] Following the conversion of the lipidic biomass to free
fatty acids, the FFAs are converted to straight-chain paraffins
(i.e., n-alkanes) via a reduction process. This step can be carried
out in the gas phase (e.g., using a fixed bed catalyst) or in the
liquid phase (e.g., using a stirred autoclave reactor with a
catalyst slurry/dispersion).
[0072] Although reduction processes have been previously performed,
the present invention recognizes that catalytic reduction processes
are needed to provide reliable, consistent decarboxylation of the
FFAs to provide a constant stream of n-alkanes, which are then
hydrocracked and, optionally, isomerized and/or hydrotreated.
Accordingly, the FFAs are contacted with an appropriate catalyst.
In one embodiment, the FFAs can be passed through a fixed-bed
catalyst, such as palladium on carbon (Pd/C). In another
embodiment, the FFAs can be combined with a slurry of Pd/C in a
stirred autoclave using solvent.
[0073] Deoxygenation is generally understood as relating to a
chemical reaction resulting in the removal of oxygen. In the
present invention, deoxygenation of FFAs is a reversible
reaction.
[0074] While decarboxylation and decarbonylation will both proceed
over a Pd/C catalyst, decarboxylation is the primary reaction
pathway, and the rate of decarboxylation is generally at least an
order of magnitude faster than that of decarbonylation. When the
n-alkane reaction product from the deoxygenation reaction is used
as the reaction solvent (which is more fully described below) and
the deoxygenation reaction is performed under hydrogen, the
decarbonylation pathway is more significant, since it is not slowed
due to microscopic reversibility. It is notable, however, that
stearic acid decarboxylation is much slower in heptadecane solvent
with a 10% H.sub.2 atm. The reaction is driven toward the reaction
product by constant 10% H.sub.2 sparge, which purges the formed
CO.sub.2 from the reactor. The decarboxylation rate is slowed in
heptadecane due to equilibrium limitations. The decarbonylation
pathway is unaffected by the change in solvent since both CO and
heptadecane are kept at low concentrations keeping the reverse
decarbonylation reactions to a minimum.
[0075] This reaction pathway can generically be referred to as a
reduction reaction or a deoxygenation reaction. Both terms are
meant to encompass both the decarboxylation reaction and the
decarbonylation reaction. Since decarboxylation is the primary
reaction pathway, particularly when using preferred catalysts, the
discussion relating to conversion of FFAs to n-alkanes may be
particularly described in terms of the decarboxylation reaction.
However, the invention is not to be considered as being limited to
decarboxylation. Rather, a decarbonylation mechanism is fully
encompassed by the invention, particularly in embodiments where
n-alkane product is recycled as the reaction solvent.
[0076] Although decarboxylation can be achieved through application
of high heat in the presence of a high boiling solvent, such
thermal decarboxylation is ineffective for complete and consistent
reaction of FFAs into their corresponding n-alkanes. In comparison,
however, catalytic decarboxylation according to the present
invention provides for very good selectivity and a conversion rate
approaching 100%. In specific embodiments, the catalytic
decarboxylation has a conversion rate to the corresponding n-alkane
of at least about 70%, at least about 75%, at least about 80%, at
least about 85%, at least about 90%, at least about 92%, at least
about 95%, at least about 96%, at least about 97%, at least about
98%, or at least about 99%.
[0077] The addition of catalyst apparently helps to drive the
reaction to completion. Accordingly, in one embodiment,
decarboxylation is performed using a solvent such as dodecane under
either catalytic or non-catalytic conditions, at temperatures of
around 300 C at 1.5 MPa pressure for varying residence times, with
a catalyst such as 5% Pd/C.
[0078] Decarboxylation of carboxylic acids was first reported by
Maier, et al. (Chemische Berichte 115: 225-229, 1982) using
gas-solid (heterogeneous) catalysis over supported palladium and
nickel catalysts in the presence of hydrogen. For straight-chain
carboxylic acids, palladium was preferred over nickel. The longest
straight-chain acid investigated by Maier et al. was octanoic acid
(C.sub.8). According to the present invention, however, it is
possible to successfully decarboxylate a longer chain carboxylic
acid (e.g., C18 compounds, such as stearic acid, or even higher
carbon compounds) in the gas phase. Such gas phase decarboxylation
generally comprises vaporization of the lipidic feedstock. For
example, in one embodiment when using a feedstock comprising
stearic acid, it is necessary to heat to a temperature of at least
about 361 C (the boiling point of stearic acid).
[0079] Gas phase catalytic deoxygenation can be carried out by
injecting the FFAs from the hydrolysis step into a suitable reactor
vessel in fluid communication with a catalyst chamber and heating
to a temperature suitable to vaporize the FFAs. The vaporized FFAs
move through the catalyst chamber where conversion to the
corresponding n-alkane on the order of 100% is achieved. The
product can then proceed through a cooling zone for condensation of
the n-alkanes. In certain embodiments, it can be useful to purge
the system with H.sub.2 to remove oxygen prior to heating to the
FFA vaporization temperature.
[0080] Liquid phase deoxygenation is also effective according to
the present invention. For example, stearic acid or other fatty
acids in a dodecane or other alkane solvent can be heated to about
300 C while contacted with a palladium catalyst, such as a 5% Pd/C
catalyst. Heptadecane is formed as the major reaction product.
Thus, when such a typical solvent is used, it is necessary to
isolate the reaction product from the solvent prior to introducing
the reaction product into the hydrocracker.
[0081] Supercritical water can optionally be used as the
solvent.
[0082] Snare, et al. (Industrial Engineering Chemistry Research
45(16): 5708-5715, 2006) investigated the deoxygenation of stearic
acid as an alternative process for biodiesel production from FFAs
using a liquid-phase batch process with dodecane as the solvent
(requiring a solvent-to-FFA mass ratio of 19:1). As pointed out
above, a separation process was required to recover the products
and remove the solvent. According to the present invention,
however, it is possible to carry out liquid phase decarboxylation
of stearic acid in heptadecane, which is the decarboxylation
product of stearic acid. Thus, in certain embodiments, the present
invention provides for liquid phase catalytic decarboxylation of a
long chain FFA into its corresponding n-alkane while recycling a
portion of the reaction product as the solvent. Employing the
product of the reaction as the solvent greatly increases the
thermodynamic efficiency because the need to heat a separate
solvent stream is eliminated. This is further advantageous because
it eliminates the need for an additional separation process because
the product and the solvent are the same. Thus, the continuous
nature of the inventive process is conserved by recycling a portion
of the decarboxylation reaction stream as the decarboxylation
solvent in a liquid phase reaction.
[0083] As previously noted, deoxygenation is a reversible process,
and there can thus be equilibrium limitations on the
decarboxylation and/or decarbonylation reactions taking place. For
example, when using recycled n-alkane reaction product as reaction
solvent, deoxygenation can be slowed in both the decarboxylation
and decarbonylation pathways. Accordingly, in certain embodiments,
it is beneficial to including a purging step to facilitate
reaction. For example, removal of CO.sub.2 (a decarboxylation
product) can be useful to drive equilibrium toward reactants.
[0084] Since decarboxylation is the dominant deoxygenation pathway
over a Pd/C catalyst, hydrogen generally is not required for the
reaction. Nevertheless, in specific embodiments, it can be
particularly useful to introduce hydrogen into the reaction.
[0085] The decarboxylation kinetics of stearic acid and oleic acids
in H.sub.2 are closely similar, with complete FFA conversion
occurring in approximately 30 minutes and providing essentially
100% yield of n-heptadecane.
[0086] Other known processes that purport to form fuels rely
heavily on the use of H.sub.2 as a reactant, particularly in
hydrotreating processes, to achieve oxygen removal. The present
invention, however, is not so limited. Rather, as pointed out
above, deoxygenation according to the present process is
catalytically achieved, and amount of H.sub.2 used is generally a
function of the lipidic biomass feedstock. For example, when using
highly saturated materials, H.sub.2 can be relegated to a basically
non-reactive status, being used mainly as a purge material, such as
described above in relation to gas-phase catalytic decarboxylation.
When using a less saturated (i.e., more olefinic) feedstock,
additional H.sub.2 can be used to encourage production of
n-alkanes.
[0087] While Pd/C can be used as an efficient FFA decarboxylation
catalyst, the use of other catalysts is not excluded. Rather, any
catalyst effective in facilitating FFA decarboxylation can be used
as a catalyst, or, alternatively, no catalyst need be used. In
particular, any noble metal may be used, particularly platinum and
palladium. Moreover, bimetallic catalysts may also be used
according to the invention and may have the formula M.sub.N-X,
wherein M.sub.N is a noble metal and X is a complementary metal,
which can include other noble metals or transition metals.
Moreover, supports other than carbon can be used according to the
invention. Non-limiting examples of supports useful according to
the invention in addition to carbon include silicates, as well as
any other support-type material which, preferably, is non-acidic
and substantially or completely inert (i.e., have little or no
inherent catalytic function). Non-limiting examples of further
catalysts that could be used according to the invention include Ni,
Ni/Mo, Ru, Pd, Pt, Ir, Os, and Rh metal catalysts.
[0088] By using a catalyst, the temperature requirements are
generally lower than when no catalyst is used, although the
decarboxylation is still performed when no catalysts are present.
In the absence of a catalyst, temperatures in excess of 400 C are
typically used to achieve appreciable decarboxylation. Even greater
temperatures (e.g., in excess of 500 C) can be required to achieve
useful levels of decarboxylation. The use of catalysts, therefore,
can be preferred. Particularly, it is possible to proceed with
significantly lower reaction temperatures while still achieving
excellent decarboxylation. In certain embodiments, to carry out
catalytic decarboxylation in a liquid phase reaction, the FFAs are
heated to a temperature of up to about 325 C. In other embodiments,
the FFAs are heated, in the presence of a suitable catalyst, to a
temperature in the range of about 200 C to about 320 C, about 250 C
to about 320 C., about 270 C to about 320 C, or about 290 C to
about 310 C. Reaction pressure can be in the range of about 400 kPa
to about 800 kPa, preferably about 500 kPa to about 700 kPa.
[0089] Catalytic decarboxylation occurs at around 300 C in the
liquid-phase under conditions, where this temperature may be too
low to achieve thermal decarboxylation in the absence of a
catalyst. Moreover, reaction selectivity for n-alkanes. For
example, in certain embodiments, decarboxylation occurs in a manner
such that greater than 90% of the hydrocarbon reaction products are
n-alkanes. In further embodiments, decarboxylation occurs in a
manner such that greater than 92%, greater than 95%, greater than
97%, or greater than 98% of the hydrocarbon reaction products are
n-alkanes.
[0090] The largest single energy cost in the process of the
invention is the cost of heating the solvent to reaction
temperature. Accordingly, in preferred embodiments, the inventive
process can be optimized to minimize or eliminate the use of an
added solvent in the reaction process. In one particular
embodiment, the reaction can proceed in liquid n-alkane (without
additional solvent) that is recycled from the reaction process. In
such an embodiment, the catalyst can be used in a slurry/dispersion
with the FFAs. Moreover, since the decarboxylation is proceeding
catalytically and is not dependent upon temperature alone, less
heat is required to maintain the lower process heat used in the
catalytic decarboxylation process.
[0091] The benefits of thermal decarboxylation are particularly
seen in the liquid phase reaction using recycled n-alkane as the
reaction solvent. As pointed out above, traditional thermal
decarboxylation is typically carried out in the liquid phase using
a hydrocarbon solvent, such as dodecane. By using a portion of the
n-alkane that is produced as the solvent for the decarboxylation
reaction, one need not separately isolate the product from the
solvent. In certain embodiments, it is possible to use a catalyst
slurry/dispersion with a solvent that is recycled n-alkane
decarboxylation reaction product.
[0092] In further embodiments, the reaction can be carried out in a
continuous stirred autoclave with recycling of reaction components.
Further, gas phase fixed bed reactors, as well as liquid phase
slurry reactors could be use. Of course, these are merely
representative types of reactors and are not intended to limit the
scope of the invention. One example of a method for heterogeneous
catalytic deoxygenation is disclosed by Snare et al., I. & E.
Chem. Res. 45(16) 5708-5715 (2006), which is incorporated herein by
reference in its entirety.
[0093] U.S. Patent Publication No. 20080071125 describes the use of
supercritical water to affect decarboxylation. Using a Diels Alder
reaction, the fatty acids (if they include double bonds) can be
cyclized before they are decarboxylated, if desired. The contents
of this patent application are hereby incorporated by reference in
their entirety.
[0094] U.S. Pat. No. 8,389,782 discloses thermal decarboxylation
reactions, and these can also be used.
[0095] The '872 patent discloses that catalysts can be used,
including metal titanates, also referred to herein interchangeably
as titanates, which can be expressed as MTiO.sub.3 wherein M is a
metal having a valence of 2+. The metal M may also be capable of
multiple valences. In one embodiment, the catalyst consists
essentially of at least a metal titanate of the formula MTiO.sub.3.
Pure metal titanates have a perovskite crystalline structure. The
catalyst can contain at least 80% by weight titanate. In another
embodiment, the catalyst contains at least 1% by weight titanate;
in another embodiment at least 5% by weight titanate; in another
embodiment at least 10% by weight titanate based on the total
weight of the catalyst, including any other desirable active
components as well as optional support material. The actual amount
of titanate needed will vary depending on whether or not a support
is used, and how the catalyst is dispersed on the support. Examples
of suitable metal titanates for use in the catalyst include, but
are not limited to, magnesium titanate, copper titanate, nickel
titanate, iron(II) titanium oxide, cobalt titanium oxide,
manganese(II) titanium oxide, lead(II) titanate, calcium titanate,
barium titanate, zinc titanate, and mixtures thereof. In one
embodiment, the catalyst has a BET surface area greater than 20
m.sup.2/g; in another embodiment the BET surface area is greater
than 200 m.sup.2/g; in yet another embodiment the BET surface area
is greater than 400 m.sup.2/g.
[0096] In one embodiment, the catalyst is a supported catalyst.
Suitable support materials include silica, alumina, silica-alumina,
carbon, molecular sieves and mixtures thereof. In one embodiment,
the catalyst is deposited on a carbon support having a BET surface
area of between 500 m.sup.2/g and 1500 m.sup.2/g. In another
embodiment, the catalyst is deposited on a support selected from
silica, alumina, silica-alumina and mixtures thereof, and the
support has a BET surface area of between 150 m.sup.2/g and 600
m.sup.2/g. In one embodiment, the support can be a monolithic
support. Alternatively, the catalyst can be unsupported.
[0097] The feed is contacted with the catalyst at a temperature of
less than 500 C, in one embodiment from 200 C to 500 C, and in one
embodiment from 200 C to 400 C. In one embodiment, the pressure
within the reactor is between 100 kPa and 1000 kPa (all pressures
indicated herein are absolute). The pressure can be below 100 kPa,
although depending on the pressure in the surrounding equipment, it
may be necessary to pump the stream exiting the reactor to a higher
pressure. In one embodiment, the LHSV is between 0.1 and 10 in
another embodiment, the LHSV is between 0.2 and 5.0 h.sup.-1; in
another embodiment, between 0.4 and 2.0 h.sup.-1. LHSV refers to
the volumetric liquid feed rate per total volume of catalyst and is
expressed in the inverse of hours (h.sup.-1).
[0098] In one embodiment, the reaction is conducted in the absence
of added hydrogen.
[0099] In the working examples, the '782 patent used ZnTiO.sub.3
(product number 634409, obtained from Sigma-Aldrich Corp., St.
Louis, Mo.) at a temperature of around 350 C in a batch reactor,
with N.sub.2 as a purge gas to remove CO.sub.2 formed during the
reaction.
Decarboxylation in Supercritical Water
[0100] The authors of the '125 application used catalytic
hydrothermolysis to both hydrolyze triglycerides and thermally
decarboxylate the fatty acids. Since fatty acids are used as
feedstocks, the hydrolysis step is not performed, but otherwise,
the conditions used for catalytic hydrothermolysis are one way to
carry out the desired thermal decarboxylation.
[0101] There is a growing interest in hot-compressed water as
alternatives to organic solvents and as a medium for unique and/or
green chemistry. Of particular interest is processes in water near
its critical point (T.sub.c=374 C, P.sub.c =221 bar, and
rho.sub.c=0.314 g/ml). One of the attractive features of
hot-compressed water is the adjustability of its properties by
varying process temperature and pressure. Specific to its solvent
properties, the dielectric constant of water can be adjusted from
80 at room temperature to 5 at its critical point. Therefore, water
can solubilize most nonpolar organic compounds including most
hydrocarbons and aromatics starting at 200-250 C and extending to
the critical point. The reversal of the solvent characteristics of
hot-compressed water also results in precipitation of salts that
are normally soluble in room temperature water. Most inorganic
salts become sparingly soluble in supercritical water. This is the
basis for unique separation of ionic species in supercritical
water. The precipitated salts can serve as heterogeneous catalysts
for reactions in supercritical water.
[0102] Hot-compressed water has been exploited in a number of novel
processes including oxidation, partial oxidation, hydrolysis, and
cracking/thermal degradation of small molecular compounds and
polymeric materials. The last processing area of this list is the
most pertinent to the process of the present invention. Studies
have already been conducted on the thermal degradation of
polyethylene in subcritical and supercritical water since the late
1990s. It has also been shown that supercritical water suppressed
coke formation and increased oil yield in cracking polyethylene as
compared to thermal cracking. As a comparison, conventional
cracking inevitably produces large fractions of coke and light
hydrocarbons. For example, catalytic cracking of palm oil without
water can achieve 99 wt % conversion, but only 48 wt % gasoline
yield at 450 C using zeolite catalysts with the balance (52%) being
coke and light hydrocarbons. The unique and established
contributions by hot-compressed water to various oxidation and
hydrolysis processes are translated to modified soybean oil in the
CH process of the present invention.
[0103] The CH process as used in the present invention can trigger
the following simultaneous or sequential reactions: cracking,
hydrolysis, decarboxylation, dehydration, isomerization,
recombination, and/or aromatization.
[0104] Cracking is the key reaction pathway to manipulate the
carbon chain length distribution and structural variation of the
resulting hydrocarbon mixture. In such a water/oil homogeneous
state and uniform and rapid heating environment provided by
hot-compressed water, the cracking reactions of the current
invention produce a more desirable spectrum of hydrocarbon products
than any conventional thermal cracking process. Unsaturated fatty
acids and derivatives are more susceptible for cracking at lower
temperatures than the saturated fatty acids. Specifically, cracking
of unsaturated fatty acids and pre-conditioned derivatives are
likely to occur at the carbon adjacent to either side of a double
bond or a junction point of three carbon-carbon bonds resulting
from cross-linking. The apparent activation energy for hydrothermal
of cracking heavy saturated hydrocarbons has a reported value of 76
Id/mol. Cracking reactions and products are summarized in the
following table.
[0105] Catalytic Decarboxylation/Dehydration oxygen, as carbon
dioxide, from fatty acids. Reactions of long chain saturated fatty
acids in hot-compressed water primarily produce alkanes and alkenes
with one less carbon than that of the starting compound.
Specifically, decarboxylation of stearic acid in supercritical
water follows monomolecular and bimolecular reaction pathways. The
former produces C.sub.17 alkane, and the latter renders C.sub.35
ketone (i.e., combining two fatty acid molecules) and C.sub.16
alkene. The formation of C.sub.35 ketone may increase C.sub.10 and
C.sub.11 fractions in the cracked hydrocarbon mixture. The presence
of a water solvent field greatly facilitates the decarboxylation
reaction. For soybean saturated fatty acids (14 wt %), mostly
palmitic acid (11 wt %), decarboxylation is likely to occur before
cracking. While decarboxylation removes carbon dioxide from the
fatty acid, the proton stays with the carbon backbone to form the
alkane. Therefore, for each mole of soybean oil, 1.5 moles of
H.sub.2 are extracted from water and added to the resulting
hydrocarbon.
[0106] Processing parameters govern the effectiveness and
efficiency of the CH process and its product quality and
distribution include temperature, water to oil ratio, catalysts,
and rate of heating and depressurization. Specifically, temperature
effects the rates of parallel reactions, hence influencing carbon
chain length distribution and characteristics. The CH process is
conducted at temperatures ranging from 240 to 450 C under
corresponding pressures either above or below the saturation or
critical pressure. The deviation of pressure from saturation or
critical pressure may be determined by process operability, product
quality and economics. In addition, isomerization and aromatization
may take place under CH conditions at the higher temperatures, in
the range of 400 to 500 C.
[0107] The water to fatty acid ratio is another key factor to
control the rates of cracking and decarboxylation, hence impacting
on product distributions. It also has process economic
implications, since more water would require more thermal energy
input. The water to oil mass ratio is controlled in the range from
10:1 to 1:100, preferably from 1:1 to 1:10.
[0108] Most catalysts used in conventional organic phase oil
conversion processes are likely to be deactivated by water,
particularly high-temperature water. Two types of materials have
been used as catalysts in high-temperature water applications:
metal oxides and inorganic salts. Catalysts suitable for use in the
CH process include salts, oxides, hydroxides, clays, minerals, and
acids. Preferably, catalysts are selected from metal oxides,
preferably transition metal oxides, such as ZrO.sub.2, TiO.sub.2
and Al.sub.2O.sub.3; high melting point salts which are insoluble
in supercritical water, such as Na.sub.2CO.sub.3, Cu.sub.2Cl.sub.2
and Cu.sub.2Br.sub.2; low melting point salts, such as ZnCl.sub.2;
hydroxides, such as alkali and alkali earth metal hydroxides; clays
such as bentonite and montmorillonite; minerals such as silicates,
carbonates, molybdates, or borates; or mineral or boric acids.
[0109] Finally, the rate of heating and depressurization of the CH
process effluent can be used to manipulate product yield and
quality. Critically, the rate of heating the fatty acids by contact
with the water should be rapid, preferably no less than 10 C per
second. Similarly, the pressure of the oil/water mixture should be
reduced before releasing the same through a nozzle, or otherwise
allowing sudden expansion, to ensure continued separation of the
oil and water.
Dehydrogenation
[0110] If the decarboxylated fatty acids do not include
carbon-carbon double bonds, and it is desirable that they do so,
they can be dehydrogenated before the olefin metathesis reaction.
Similarly, before or following the olefin metathesis, any alkanes
present in the low molecular weight olefin fraction can be
dehydrogenated. The dehydrogenation catalyst must have
dehydrogenation activity to convert at least a portion of the
paraffins to olefins, which are believed to be the actual species
that undergo olefin metathesis.
[0111] Platinum and palladium or the compounds thereof are
preferred for inclusion in the dehydrogenation/hydrogenation
component, with platinum or a compound thereof being especially
preferred. As noted previously, when referring to a particular
metal in this disclosure as being useful, the metal can be present
as elemental metal or as a compound of the metal. As discussed
above, reference to a particular metal in this disclosure is not
intended to limit the invention to any particular form of the metal
unless the specific name of the compound is given, as in the
examples in which specific compounds are named as being used in the
preparations.
[0112] The dehydrogenation step can be conducted by passing the
decarboxylated fatty acids over a dehydrogenation catalyst under
dehydrogenating reaction conditions. If it is desirable to reduce
or eliminate the amount of diolefins produced or other undesired
by-products, the reaction conversion to internal olefins should
preferably not exceed 50%, and more preferably not exceed 30%, but
proceed by at least 15-20%.
[0113] The dehydrogenation is typically conducted at temperatures
between about 500 F and 1000 F (260 C and 538 C), preferably
between about 600 F and 800 F (316 C and 427 C). The pressures are
preferably between about 0.1 and 10 atms, more preferably between
about 0.5 and 4 atms absolute pressure (about 0.5 to 4 bars). The
LHSV (liquid hourly space velocity) is preferably between about 1
and 50 hr.sup.-1, preferably between about 20 and 40 hr.sup.-1. The
products generally and preferably include internal olefins.
[0114] The dehydrogenation is also typically conducted in the
presence of a gaseous diluent, typically and preferably hydrogen.
Although hydrogen is the preferred diluent, other art-recognized
diluents may also be used, either individually or in admixture with
hydrogen or each other, such as steam, methane, ethane, carbon
dioxide, and the like. Hydrogen is preferred because it serves the
dual-function of not only lowering the partial pressure of the
dehydrogenatable hydrocarbon, but also of suppressing the formation
of hydrogen-deficient, carbonaceous deposits on the catalytic
composite. Hydrogen is typically used in amounts sufficient to
insure a hydrogen to hydrocarbon feed mole ratio of about from 2:1
to 40:1, preferably in the range of about from 5:1 to 20:1.
[0115] Suitable dehydrogenation catalysts which can be used include
Group VIII noble metals, e.g., iron, cobalt, nickel, palladium,
platinum, rhodium, ruthenium, osmium, and iridium, preferably on an
oxide support.
[0116] Less desirably, combinations of Group VIII non-noble and
Group VIB metals or their oxides, e.g., chromium oxide, may also be
used. Suitable catalyst supports include, for example, silica,
silicalite, zeolites, molecular sieves, activated carbon alumina,
silica-alumina, silica-magnesia, silica-thoria, silicaberylia,
silica-titania, silica-aluminum-thora, silica-alumina-zirconia
kaolin clays, montmorillonite clays and the like. In general,
platinum on alumina or silicalite afford very good results in this
reaction. Typically, the catalyst contains about from 0.01 to 5 wt.
%, preferably 0.1 to 1 wt. % of the dehydrogenation metal (e.g.,
platinum). Combination metal catalysts, such as those described in
U.S. Pat. Nos. 4,013,733; 4,101,593 and 4,148,833, can be used.
[0117] Since dehydrogenation produces a net gain in hydrogen, the
hydrogen may be taken off for other plant uses or as is typically
the case, where the dehydrogenation is conducted in the presence of
hydrogen, a portion of the recovered hydrogen can be recycled back
to the dehydrogenation reactor. Further information regarding
dehydrogenation and dehydrogenation catalysts can, for example, be
found in U.S. Pat. Nos. 4,046,715; 4,101,593; and 4,124,649. A
variety of commercial processes also incorporate dehydrogenation
processes, in their overall process scheme, which dehydrogenation
processes may also be used in the present process to dehydrogen the
paraffinic hydrocarbons. Examples of such processes include the
dehydrogenation process portion of the Pacol process for
manufacturing linear alkylbenzenes, described in Vora et al.,
Chemistry and Industry, 187-191 (1990); Schulz R. C. et al., Second
World Conference on Detergents, Montreaux, Switzerland (October
1986); and Vora et al., Second World Surfactants Congress, Paris
France (May 1988).
[0118] If desired, diolefins produced during the dehydrogenation
step may be removed by known adsorption processes or selective
hydrogenation processes which selectively hydrogenate diolefins to
monoolefins without significantly hydrogenating monoolefins. One
such selective hydrogenation process known as the DeFine process is
described in the Vora et al. Chemistry and Industry publication
cited above. [0119] A. Isomerization Chemistry
[0120] Optionally, various fractions resulting from the thermal
decarboxylation of free fatty acids (i.e., a fraction already in
the desired molecular weight range for preparing the desired
distillate fuel product), the fractions being molecularly averaged,
and/or the products of the molecular averaging chemistry, are
isomerized. The isomerization products have more branched
paraffins, thus improving their pour, cloud and freeze points.
Isomerization processes are generally carried out at a temperature
between 200 F and 700 F, preferably 300 F to 550 F, with a liquid
hourly space velocity between 0.1 and 2, preferably between 0.25
and 0.50. The hydrogen content is adjusted such that the hydrogen
to hydrocarbon mole ratio is between 1:1 and 5:1. Catalysts useful
for isomerization are generally bifunctional catalysts comprising a
hydrogenation component (preferably selected from the Group VIII
metals of the Periodic Table of the Elements, and more preferably
selected from the group consisting of nickel, platinum, palladium
and mixtures thereof) and an acid component. Examples of an acid
component useful in the preferred isomerization catalyst include a
crystalline zeolite, a halogenated alumina component, or a
silica-alumina component. Such paraffin isomerization catalysts are
well known in the art.
[0121] Optionally, but preferably, the resulting product is
hydrogenated. The hydrogen can come from a separate hydrogen plant,
can be derived from syngas, made directly from methane or other
light hydrocarbons, or come directly from the thermal
decarboxylation step.
[0122] After hydrogenation, which typically is a mild
hydrofinishing step, the resulting distillate fuel product is
highly paraffinic. Hydrofinishing is done after isomerization.
Hydrofinishing is well known in the art and can be conducted at
temperatures between about 190 C to about 340 C, pressures between
about 400 psig to about 3000 psig, space velocities (LHSV) between
about 0.1 to about 20, and hydrogen recycle rates between about 400
and 1500 SCF/bbl.
[0123] The hydrofinishing step is beneficial in preparing an
acceptably stable fuel. Fuels that do not receive the
hydrofinishing step may be unstable in air and light due to olefin
polymerization. To counter this, they may require higher than
typical levels of stability additives and antioxidants. [0124] B.
Thermal Cracking
[0125] The thermal decarboxylation products are subjected to
hydrocracking steps, to reduce their molecular weight, and,
ideally, to reduce the viscosity of the products to be the same as,
or lower than, diesel fuel. The viscosity can be lowered by
thermally cracking, hydrocracking, or pyrolyzing the composition,
preferably in the presence of a Lewis acid catalyst.
[0126] Methods for thermally cracking or hydrocracking hydrocarbons
are known to those of skill in the art. Representative Lewis acid
catalysts and reactions conditions are described, for example, in
Fluid Catalytic Cracking II, Concepts in Catalyst Design, ACS
Symposium Series 452, Mario Occelli, editor, American Chemical
Society, Washington, D.C., 1991. The pyrolysis of vegetable oils is
described in Alencar, et al., Pyrolysis of Tropical Vegetable Oils,
J. Ag. Food Chem., 31:1268-1270 (1983). The hydrocracking of
vegetable oils is described in U.S. Pat. No. 4,992,605 to Craig, et
al.
[0127] In one embodiment, the fuel additive composition is heated
to a temperature of between approximately 100 and 500 F, preferably
to between approximately 100 and 200 F, and more preferably to
between approximately 150 and 180 F, and then passed through a
Lewis acid catalyst. Any Lewis acid catalyst that is effective for
thermally cracking hydrocarbons can be used. Suitable catalysts for
use in the present invention include, but are not limited to,
zeolites, clay montmorrilite, aluminum chloride, aluminum bromide,
ferrous chloride and ferrous bromide. Preferably, the catalyst is a
fixed-bed catalyst.
[0128] A preferred catalyst is prepared by coating a ceramic
monolithic support with lithium metal. Supports of this type are
manufactured, for example, by Dow-Coming. Lithium is coated on the
support by first etching the support with zinc chloride, then
brushing lithium onto the support, and then baking the support.
[0129] The retention time through the Lewis acid catalyst can be as
little as one second, although longer retention times do not
adversely affect the product.
[0130] After passing through the Lewis acid catalyst, the
derivative stream is then preferably heated to a temperature of
between approximately 200 and 600 F, preferably between
approximately 200 and 230 F, to thermally crack the product. The
resulting product is suitable for blending with distillate fuel,
such as gasoline, diesel, or jet fuel, to form an alternative fuel
composition. [0131] C. Hydrotreating and/or Hydrocracking
Chemistry
[0132] Fractions used in the process described herein may include
heteroatoms such as sulfur or nitrogen, diolefins and alkynes that
may adversely affect the catalysts used in the various reactions.
If sulfur impurities are present in the starting materials, they
can be removed using means well known to those of skill in the art,
for example, extractive Merox, hydrotreating, adsorption, etc.
Nitrogen-containing impurities can also be removed using means well
known to those of skill in the art. Hydrotreating and hydrocracking
are preferred means for removing these and other impurities from
the heavy wax feed component. Removal of these components from the
light naphtha and gas streams must use techniques that minimize the
saturation of the olefins in these streams. Extractive Merox is
suitable for removing sulfur compounds and acids from the light
streams. The other compounds can be removed, for example, by
adsorption, dehydration of alcohols, and selective hydrogenation.
Selective hydrogenation of diolefins, for example, is well known in
the art. One example of a selective hydrogenation of diolefins in
the presence of olefins is UOP's DeFine process.
[0133] Hydrogenation catalysts can be used to hydrotreat the
products resulting from the hydrocracking and/or isomerization
reactions.
[0134] As used herein, the terms "hydrotreating" and
"hydrocracking" are given their conventional meaning and describe
processes that are well known to those skilled in the art.
Hydrotreating refers to a catalytic process, usually carried out in
the presence of free hydrogen, in which the primary purpose is the
desulfurization and/or denitrification of the feedstock. Generally,
in hydrotreating operations, cracking of the hydrocarbon molecules,
i.e., breaking the larger hydrocarbon molecules into smaller
hydrocarbon molecules, is minimized and the unsaturated
hydrocarbons are either fully or partially hydrogenated.
[0135] Hydrocracking refers to a catalytic process, usually carried
out in the presence of free hydrogen, in which the cracking of the
larger hydrocarbon molecules is a primary purpose of the operation.
Desulfurization and/or denitrification of the feed stock usually
will also occur.
[0136] Catalysts used in carrying out hydrotreating and
hydrocracking operations are well known in the art. See, for
example, U.S. Pat. Nos. 4,347,121 and 4,810,357 for general
descriptions of hydrotreating, hydrocracking, and typical catalysts
used in each process.
[0137] Suitable catalysts include noble metals from Group VIIIA,
such as platinum or palladium on an alumina or siliceous matrix,
and unsulfided Group VIIIA and Group VIB, such as nickel-molybdenum
or nickel-tin on an alumina or siliceous matrix. U.S. Pat. No.
3,852,207 describes suitable noble metal catalysts and mild
hydrotreating conditions. Other suitable catalysts are described,
for example, in U.S. Pat. Nos. 4,157,294 and 3,904,513. The
non-noble metal (such as nickel-molybdenum) hydrogenation metal are
usually present in the final catalyst composition as oxides, or
more preferably or possibly, as sulfides when such compounds are
readily formed from the particular metal involved. Preferred
non-noble metal catalyst compositions contain in excess of about 5
weight percent, preferably about 5 to about 40 weight percent
molybdenum and/or tungsten, and at least about 0.5, and generally
about 1 to about 15 weight percent of nickel and/or cobalt
determined as the corresponding oxides. The noble metal (such as
platinum) catalyst contains in excess of 0.01 percent metal,
preferably between 0.1 and 1.0 percent metal. Combinations of noble
metals may also be used, such as mixtures of platinum and
palladium.
[0138] The hydrogenation components can be incorporated into the
overall catalyst composition by any one of numerous procedures. The
hydrogenation components can be added to matrix component by
co-mulling, impregnation, or ion exchange and the Group VI
components, i.e., molybdenum and tungsten can be combined with the
refractory oxide by impregnation, co-mulling or co-precipitation.
Although these components can be combined with the catalyst matrix
as the sulfides, that may not be preferred, as the sulfur compounds
may interfere with some molecular averaging or Fischer-Tropsch
catalysts.
[0139] The matrix component can be of many types including some
that have acidic catalytic activity. Ones that have activity
include amorphous silica-alumina or may be a zeolitic or
non-zeolitic crystalline molecular sieve. Examples of suitable
matrix molecular sieves include zeolite Y, zeolite X and the
so-called ultra-stable zeolite Y and high structural silica:alumina
ratio zeolite Y such as that described in U.S. Pat. Nos. 4,401,556,
4,820,402 and 5,059,567. Small crystal size zeolite Y, such as that
described in U.S. Pat. No. 5,073,530, can also be used.
Non-zeolitic molecular sieves which can be used include, for
example, silicoaluminophosphates (SAPO), ferroaluminophosphate,
titanium aluminophosphate, and the various ELAPO molecular sieves
described in U.S. Pat. No. 4,913,799 and the references cited
therein. Details regarding the preparation of various non-zeolite
molecular sieves can be found in U.S. Pat. No. 5,114,563 (SAPO);
U.S. Pat. No. 4,913,799 and the various references cited in U.S.
Pat. No. 4,913,799. Mesoporous molecular sieves can also be used,
for example, the M415 family of materials (J. Am. Chem. Soc. 1992,
114, 10834-10843), MCM-41 (U.S. Pat. Nos. 5,246,689, 5,198,203 and
5,334,368), and MCM-48 (Kresge et al., Nature 359 (1992) 710).
[0140] Suitable matrix materials may also include synthetic or
natural substances as well as inorganic materials such as clay,
silica and/or metal oxides such as silica-alumina, silica-magnesia,
silica-zirconia, silica-thoria, silica-berylia, silica-titania as
well as ternary compositions, such as silica-alumina-thoria,
silica-alumina-zirconia, silica-alumina-magnesia, and
silica-magnesia zirconia. The latter may be either naturally
occurring or in the form of gelatinous precipitates or gels
including mixtures of silica and metal oxides. Naturally occurring
clays which can be composited with the catalyst include those of
the montmorillonite and kaolin families. These clays can be used in
the raw state as originally mined or initially subjected to
calumniation, acid treatment or chemical modification.
[0141] Furthermore, more than one catalyst type may be used in the
reactor. The different catalyst types can be separated into layers
or mixed. Typical hydrotreating conditions vary over a wide range.
In general, the overall LHSV is about 0.25 to 2.0, preferably about
0.5 to 1.0. The hydrogen partial pressure is greater than 200 psia,
preferably ranging from about 500 psia to about 2000 psia. Hydrogen
recirculation rates are typically greater than 50 SCF/Bbl, and are
preferably between 1000 and 5000 SCF/Bbl. Temperatures range from
about 300 F to about 750 F, preferably ranging from 450 F to 600 F.
[0142] D. Filtration of the Fuel Composition
[0143] In one embodiment, the fuel composition is filtered,
preferably through a filter with a pore size of between
approximately 5 and 50 microns, more preferably, between
approximately 10 and 20 microns, to remove solid impurities. This
can be especially important when animal fats are used, since
rendering processes can inadvertently place small pieces of bone
and other particulate matter in the animal fat that needs to be
removed.
[0144] Modifications and variations of the present invention will
be obvious to those skilled in the art from the foregoing detailed
description of the invention. The disclosures of each of the
patents and papers discussed above are incorporated herein by
reference in their entirety.
* * * * *