U.S. patent application number 14/520757 was filed with the patent office on 2015-02-05 for process for producing mixed esters of fatty acids as biofuels.
The applicant listed for this patent is BOARD OF TRUSTEES OF MICHIGAN UNIVERSITY. Invention is credited to Navinchandra S. Asthana, Evan Bittner, Carl T. Lira, Dennis J. Miller.
Application Number | 20150033618 14/520757 |
Document ID | / |
Family ID | 40640493 |
Filed Date | 2015-02-05 |
United States Patent
Application |
20150033618 |
Kind Code |
A1 |
Asthana; Navinchandra S. ;
et al. |
February 5, 2015 |
PROCESS FOR PRODUCING MIXED ESTERS OF FATTY ACIDS AS BIOFUELS
Abstract
A process for producing mixed esters of fatty acids as biofuel
or additive to a petroleum fuel for use in a compression ignition
(CI) engine. The process preferably provides a partial
transesterification of a mixture of fatty acid methyl esters with
at least one alkyl alcohol containing 2 to 8 carbon atoms in the
presence of a heterogeneous solid acid catalyst to produce a
mixture of the fatty acid methyl esters and alkyl alcohol esters of
the fatty acids.
Inventors: |
Asthana; Navinchandra S.;
(Evansville, IN) ; Miller; Dennis J.; (Okemos,
MI) ; Lira; Carl T.; (East Lansing, MI) ;
Bittner; Evan; (Duluth, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BOARD OF TRUSTEES OF MICHIGAN UNIVERSITY |
East Lansing |
MI |
US |
|
|
Family ID: |
40640493 |
Appl. No.: |
14/520757 |
Filed: |
October 22, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14077897 |
Nov 12, 2013 |
8894725 |
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14520757 |
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12313343 |
Nov 19, 2008 |
8613780 |
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14077897 |
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61003790 |
Nov 20, 2007 |
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Current U.S.
Class: |
44/398 ; 44/401;
44/402 |
Current CPC
Class: |
C10L 2300/20 20130101;
C10G 2300/1011 20130101; C10L 2300/30 20130101; C10L 2200/0469
20130101; Y02P 30/20 20151101; C10L 1/026 20130101; C10L 1/19
20130101; Y02E 50/10 20130101; C10L 10/14 20130101; Y02E 50/13
20130101 |
Class at
Publication: |
44/398 ; 44/401;
44/402 |
International
Class: |
C10L 10/14 20060101
C10L010/14; C10L 1/02 20060101 C10L001/02 |
Claims
1-24. (canceled)
25. A composition useful in a compression ignition (CI) engine, the
composition comprising: a mixture comprising (a) fatty acid methyl
esters and (b) fatty acid alkyl esters of at least one alkyl
alcohol containing 2 to 8 carbon atoms, wherein: (i) the mixture
has a cloud point that is lower in temperature than that of a
mixture comprising the fatty acid methyl esters alone, and (ii) the
composition has a cloud point ranging from -4.degree. C. to
-12.degree. C.
26. The composition of claim 25 wherein the fatty acid methyl
esters and the fatty acid alkyl esters comprise esters of palmitic
acid, stearic acid, oleic acid, linoleic acid, and linolenic acid
from soybean oil.
27. The composition of claim 25 further comprising an ester of a
fermentation or non-fermentation derived organic acid with at least
one alkyl alcohol containing 1 to 6 carbon atoms.
28. The composition of claim 27 wherein the ester comprises
dimethyl succinate.
29. The composition of claim 27 wherein the ester is derived from
an acid selected from the group consisting of lactic acid, succinic
acid, and mixtures thereof.
30. The composition of claim 27 wherein the ester is derived from
an acid selected from the group consisting of propionic acid,
butyric acid, isobutyric acid, and mixtures thereof.
31. The composition of claim 27 further comprising an ether
selected from the group consisting of dibutyl ether (DBE); methyl
tert-butyl ether (MTBE); tertiary amyl methyl ether (TAME);
tertiary hexyl methyl ether (THEME); ethyl tertiary butyl ether
(ETBE); tertiary amyl ethyl ether (TAEE); propyl ether (DIPE);
dipropyl ether; dihexyl ether; dioctyl ether, and
iso-amyl-ether.
32. The composition of claim 27 further comprising an ether
containing at least 6 carbon atoms.
33. The composition of claim 25 wherein the fatty acid alkyl esters
of at least one alkyl alcohol containing 2 to 8 carbon atoms
comprise fatty acid ethyl esters.
34. The composition of claim 25 wherein the fatty acid alkyl esters
of at least one alkyl alcohol containing 2 to 8 carbon atoms
comprise fatty acid butyl esters.
35. The composition of claim 25 wherein the fatty acid alkyl esters
of at least one alkyl alcohol containing 2 to 8 carbon atoms
comprise fatty acid ethyl esters and fatty acid butyl esters.
36. The composition of claim 25 wherein the mixture has a cloud
point that is 5.degree. C. to 10.degree. C. lower than that of a
mixture comprising the fatty acid methyl esters alone.
37. The composition of claim 25 wherein the mixture has a cloud
point that is 5.degree. C. to 14.degree. C. lower than that of a
mixture comprising the fatty acid methyl esters alone.
38. The composition of claim 25 wherein a volume ratio between the
fatty acid methyl esters and the fatty acid alkyl esters of at
least one alkyl alcohol containing 2 to 8 carbon atoms ranges from
6:94 to 34:66 in the composition.
39. The composition of claim 25 wherein the fatty acid methyl
esters are present in an amount ranging from 3% to 34% of the
composition.
40. The composition of claim 25 wherein the fatty acid methyl
esters are present in an amount ranging from 3% to 6% of the
composition.
41. The composition of claim 25 wherein the fatty acid alkyl esters
of at least one alkyl alcohol containing 2 to 8 carbon atoms are
present in an amount ranging from 47% to 94% of the
composition.
42. The composition of claim 25 further comprising a petroleum
diesel fuel present in an amount ranging from 50% to 95% of the
composition.
43. The composition of claim 25 further comprising glycerol.
44. A composition useful in a compression ignition (CI) engine, the
composition comprising: a mixture comprising (a) fatty acid methyl
esters and (b) fatty acid alkyl esters of at least one alkyl
alcohol containing 2 to 8 carbon atoms, wherein the mixture has a
cloud point that is 5.degree. C. to 14.degree. C. lower than that
of a mixture comprising the fatty acid methyl esters alone.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Priority is claimed to Provisional Application No.
61/003,790, filed Nov. 20, 2007, the entire disclosure of which is
herein incorporated by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
[0003] (1) Field of the Invention
[0004] The present invention relates generally to a process
producing mixed esters of fatty acids as biofuels particularly for
use in a compression ignition (CI) (particularly diesel)
engine.
[0005] (2) Description of Related Art
[0006] Biodiesel has been considered as an alternative to petroleum
based diesel for many years. Biodiesel is a general term referring
to a fuel comprising methyl-esters of long chain fatty acids
derived typically from vegetable oils or animal fats. It can be
used per se as fuel, or as an additive in a blend with
petroleum-based diesel fuel.
[0007] The biodiesel industry in the U.S. currently suffers from a
lack of consumer confidence in the quality of the biofuel. The
uncertainty in fuel quality stems from lack of experience on the
part of producers in being consistent in their production methods,
and the all-too-often absence of careful fuel analysis to ensure
that quality standards such as ASTM specifications are achieved.
Although several measures of biodiesel quality can be used, the
limiting factor is often the cold-weather performance properties of
biodiesel, manifested as a cloud point and pour point temperature
that is too high for the climate. A high cloud point temperature in
biodiesel is typically observed because of (1) glyceride impurities
present and (2) the presence of only methyl esters of unsaturated
and saturated fatty acids. If residual glyceride impurities are not
removed from the finished product, the biodiesel forms crystals at
low temperature and those crystals plug fuel filters and injectors.
Even if the impurities are removed, the saturated fatty acid methyl
esters crystallize at some point as temperature is reduced, thus
leading to solids formation. Thus, auto and diesel engine
manufacturers at present will only warrant biofuel compositions up
to a biofuel content of B5 (5% biodiesel/95% petroleum). Ideally, a
high quality biofuel for the North American climate would contain
at least B20 (20% biodiesel, 80% petroleum).
[0008] Biodiesel offers several advantages. In particular, when
compared to petroleum diesel, biodiesel provides similar fuel
economy, horsepower and torque while providing superior lubricity.
Moreover, biodiesel provides a substantial reduction of emission of
unburned hydrocarbons, carbon monoxide, and particulate matter.
Typically, it is free of sulfur and aromatics which are major
pollutants. Accordingly, biodiesel is considered a renewable,
non-toxic and biodegradable fuel alternative or additive.
[0009] Previous methods associated with producing mixed esters of
fatty acids include reaction of (1) a mixture of different
triglycerides with methanol; or (2) an oil (triglycerides) with a
mixture of different alcohols, namely ethanol, methanol, n-butanol
and n-propanol, in the presence of a base catalyst chosen from
sodium hydroxide, potassium hydroxide and sodium methylate. In
presence of a base catalyst (sodium or potassium hydroxides), the
rate and extent of ester formation are directly proportional to the
formation of sodium or potassium alkoxide from the alcohol in situ
in the reaction mixture.
[0010] Upon completion of the reaction, ideally two distinct
phases, 1) glycerol (a trihydroxy alcohol) and 2) esters of fatty
acids, are observed. The following limitations are typically
associated with this process: 1) the transesterification reaction
proceeds smoothly only when methanol is used as an alcohol and
fatty acid methyl ester (FAME) is synthesized, and the reaction is
adversely affected when higher alcohols such as ethanol, n-propanol
and n-butanol are used; 2) use of higher alcohols also creates a
problem of readily separating glycerol from the alkyl esters of
fatty acids, which requires additional processing steps including
alcohol separation from the reaction mixture and dilute acid wash
to facilitate glycerol phase separation from fatty acid ester; and
3) use of base catalyst increases the prospect of soap formation
(saponification of the fatty acids) which is quite detrimental to
overall process and its economy. It is a further disadvantage of
existing processes that the base catalysts used in the reaction
system are not re-usable, thereby generating a considerably
significant quantity of salt waste.
[0011] U.S. Patent Application No. 2007/0056213 to French et al.
describes a method which includes operating a two-stroke engine
with a lubricating fuel. A fuel/lubricant formulation is disclosed
for the operation of the two-stroke engines with improved emissions
and performance. The lubricating fuel includes at least one fuel
selected from the group including C1-6 alcohol, gasoline, ether,
ketone, nitromethane, and a mixture thereof, and at least one
lubricant selected from the group including biodiesel, lipid fatty
acid alkyl ester, fatty acid and a mixture thereof. Diesel fuels
are not described.
[0012] Patent application WO 2006/107407 to Clements describes
processes and systems for producing biodiesel or fatty acid esters
from multiple triglyceride feedstocks using a two step reaction
with an alcohol and acid catalyst and then an alkaline catalyst.
The first step forms an acid alcohol layer and an
ester-triglyceride layer. The second step reacts the ester
triglyceride layer with a base to form the fatty acid esters.
[0013] Patent application WO 2006/128881 to Despeghel describes
alkyl-ester compositions derived from rapeseed and sunflower, in
particular from Brassica napus and Helianthus annuus using an acid
catalyst in a batch process. Despeghel further discloses a process
for preparation of the alkyl-esters. The alkyl-ester compositions
can be used in diesel engines in its pure form or blended with
another composition such as fuel.
[0014] U.S. Pat. No. 6,468,319 to Yeh et al. describes various
esters used in diesel fuel to reduce emissions. U.S. Pat. No.
5,268,008 to Kanne describes esters used in diesel fuels to reduce
emissions.
[0015] While the related art teach processes for generating
biodiesel, there still exists a need for improved processes and
compositions for generating biodiesel.
OBJECTS
[0016] Therefore, it is an object of the present invention to
provide a biodiesel composition and an improved process for
generating the composition. The process produces an improved
biofuel which comprises in part or in whole mixed alkyl esters of
fatty acids. The invention provides a process that can be added to
current biodiesel production facilities, with the goal of removing
impurities from the biodiesel stream and at the same time producing
a mixed alkyl ester fuel with superior properties.
[0017] These and other objects of the present invention will become
increasingly apparent with reference to the following drawing and
preferred embodiments.
SUMMARY OF THE INVENTION
[0018] The present invention provides a continuous process for
producing a fatty acid alkyl ester mixture which comprises: (a)
countercurrently reacting a fatty acid methyl ester at a
temperature between about 50 and 200.degree. C. and a pressure
between about 0.5 and 20 atmospheres with at least one alkyl
alcohol having 2 to 8 carbon atoms in the presence of a solid acid
catalyst in a reactive zone in a distillation column to produce a
fatty acid alkyl ester mixture; and (b) recovering the produced
fatty acid alkyl ester mixture at the bottom of the column and the
alcohol from the top of the column. In further embodiments, the
solid acid catalyst is a heterogeneous acid catalyst. In further
still embodiments, the reactive distillation column comprises: (a)
the reactive zone containing the solid acid catalyst; (b) a fatty
acid ester inlet above the catalyst; (c) an alcohol inlet below the
catalyst; (d) product outlet at the bottom of the column for
separating the produced fatty acid alkyl ester; and (e) an outlet
at the top of the column for methanol formed in the reaction and at
least one alcohol which is unreacted. In still further embodiments,
the solid catalyst is a heterogeneous solid acid catalyst. In
further still embodiments, the fatty acid methyl ester comprises a
mixture of fatty acid methyl esters and methanol, monoglyceride,
diglyceride, triglyceride, and glycerol as impurities. In further
still embodiments, the present disclosure provides for a process
wherein at least the monoglyceride, diglyceride and triglyceride of
the impurities are transesterified in the reaction with the alkyl
alcohol having 2 to 8 carbon atoms producing mixed fatty acid alkyl
esters to be separated at the bottom of the column, along with
glycerol. The glycerol leaving the column at the bottom can be at
least partially removed by a process selected from the group
consisting of phase separation, water washing, and application of
an adsorbent.
[0019] In an exemplary embodiment, the fatty acid methyl ester is
generated from a preliminary transesterification reaction of a
vegetable oil as a triglyceride with methanol. In further still
embodiments, the preliminary transesterification reaction of a
vegetable oil as a triglyceride with methanol takes place in a
biodiesel production plant and the reactive distillation column is
added onto the biodiesel production plant to receive the fatty acid
methyl ester product stream. In further still embodiments, the
fatty acid alkyl ester produced is in admixture with the fatty acid
methyl ester. In still further embodiments, the alkyl alcohol is
ethanol and the fatty acid alkyl ester is a fatty acid ethyl ester.
In further still embodiments, the alkyl alcohol is a mixture of
alcohols having 2 to 8 carbon atoms. In still further embodiments,
the alkyl alcohol mixture contains ethanol and butanol and the
fatty acid alkyl ester produced comprises a mixture of a fatty acid
ethyl ester and a fatty acid butyl ester. In further still
embodiments, the alkyl alcohol is selected from the group
consisting of ethanol, propanol, isopropanol, butanol, isobutanol,
amyl and iso-amyl alcohol and mixtures thereof. In still further
embodiments, the produced fatty acid alkyl ester has a cloud point
lower in temperature than the methyl fatty acid ester. In further
still embodiments, the produced fatty acid alkyl ester is in
addition blended with a petroleum diesel fuel. In still further
embodiments, the petroleum diesel fuel is 50 to 95% of the blend.
In still further embodiments, the fatty acid methyl ester is
selected from the group consisting of methyl palmitate, methyl
stearate, methyl oleate, methyl linoleate, methyl linolenate, and
mixtures thereof. In further still embodiments, the produced fatty
acid alkyl ester is derived from the group of acids selected from
the group consisting of stearic acid, oleic acid, linoleic acid,
linolenic acid, and mixtures thereof.
[0020] The present invention further provides a process for
preparing a fatty acid ester mixture, useful alone or in
combination with petroleum fuel, in a compression ignition engine,
which comprises: (a) reacting an impure fatty acid methyl ester
mixture with at least one alkyl alcohol containing 2 to 8 carbon
atoms in the presence of a base or acid wherein, the impure fatty
acid methyl ester mixture comprises fatty acid methyl ester and
methanol, one or more of a monoglyceride, a diglyceride, and a
triglyceride as impurities; wherein the reaction partially
transesterifies the impure methyl ester mixture to produce a
mixture of fatty acid alkyl esters containing 1 to 8 carbon atoms;
and (b) removing methanol formed in the reaction and unreacted
alkyl alcohol to produce the fatty acid ester mixture. In an
exemplary embodiment, the alcohol is ethanol. In further still
embodiments, at least one alcohol is ethanol and at least one of
the produced alkyl fatty acid esters is a fatty acid ethyl ester.
In still further embodiments, the impure mixture is reacted with a
mixture of two or more alcohols at least one of which is ethanol.
In further still embodiments, the mixture of alcohols comprises
ethanol and butanol and the reaction with the impure fatty acid
methyl ester mixture further produces a fatty acid ethyl ester and
a fatty acid butyl ester.
[0021] The present invention provides for an exemplary process for
producing mixed esters of fatty acids, which comprises: (a)
partially transesterifying at a temperature between about 50 and
200.degree. C. and a pressure between about 0.5 and 20 atmospheres,
a mixture of fatty acid methyl esters with at least one alkyl
alcohol containing 2 to 8 carbon atoms in the presence of a
heterogeneous solid acid catalyst to produce a mixture of the fatty
acid methyl esters and alkyl alcohol derived fatty acid esters; and
(b) separating the esters from the catalyst. In further
embodiments, the mixture of fatty acid methyl esters comprises of
methyl palmitate, methyl stearate, methyl oleate, methyl linoleate
and methyl linolenate. In still further embodiments, the alkyl
alcohol is selected from the group consisting of ethanol,
n-propanol, n-butanol, iso-amyl alcohol and mixtures thereof.
[0022] The present invention provides for a composition useful in a
compression ignition (CI) engine which comprises a mixture of fatty
acid methyl esters and of fatty acid alkyl esters of at least one
alkyl alcohol containing 2 to 8 carbon atoms, wherein the cloud
point of the mixture is lower in temperature than that of the
mixture of the fatty acid methyl esters alone. In further
embodiments, the mixture of fatty acid methyl esters comprises
esters of palmitic acid, stearic acid, oleic acid, linoleic acid
and linolenic acid from soybean.
[0023] The present invention provides for a composition adapted for
use in a compression ignition (CI) engine, comprising a mixture of
fatty acid methyl esters, fatty acid alkyl esters of at least one
alkyl alcohol containing 2 to 8 carbon atoms, esters of a
fermentation or non-fermentation derived organic acid with at least
one alkyl alcohol containing 1 to 6 carbon atoms and optionally an
ether containing at least 6 carbon atoms as an oxygenate. In
further embodiments, a cloud point of the mixture is at a lower in
temperature than that of the fatty acid methyl esters alone. In
further still embodiments, the mixture of fatty acid methyl esters
comprises methyl palmitate, methyl stearate, methyl oleate, methyl
linoleate and methyl linolenate. In still further embodiments, the
alkyl alcohol is selected from the group consisting of ethanol,
propanol, butanol, iso-amyl alcohol and mixtures thereof. In
further still embodiments, the mixture of fatty acid methyl and
alkyl esters comprises esters of palmitic acid, stearic acid, oleic
acid, linoleic acid, dimethyl succinate and linolenic acid. In
still further embodiments, the fermentation or non-fermentation
derived organic acid ester is derived from an acid selected from
the group consisting of lactic acid, succinic acid and mixtures
thereof. In still further embodiments the fermentation or
non-fermentation derived organic acid ester is derived from an acid
selected from the group consisting of propionic acid, butyric acid,
isobutyric acid, dicarboxylic and carboxylic acids, and mixtures
thereof. In still further embodiments, the ether is selected from
the group consisting of dibutyl ether (DBE); methyl tert-butyl
ether (MTBE); tertiary amyl methyl ether (TAME); tertiary hexyl
methyl ether (THEME); ethyl tertiary butyl ether (ETBE); tertiary
amyl ethyl ether (TAEE); propyl ether (DIPE); dipropyl ether;
dihexyl ether; dioctyl ether, and iso-amyl-ether. In further still
embodiments, the oxygenate is an ester.
[0024] An exemplary embodiment associated with the present
invention provides for a biofuel, for use in compression ignition
(CI) engines, comprising mixtures of fatty acid methyl esters,
fatty acid esters of at least one alcohol containing 2 to 8 carbon
atoms, esters of a fermentation derived organic acid with at least
one alcohol containing 1 to 6 carbon atoms and optionally an ether
containing at least 6 carbon atoms as an oxygenate. In an exemplary
embodiment, the fermentation derived organic acid can be derived
from a carbohydrate (such as sugar) fermentation source. The cloud
point of the mixture can be lower in temperature than that of the
fatty acid methyl esters alone (conventionally known as biodiesel
and currently used in CI engines). Typically, the mixture of fatty
acid methyl esters contains methyl palmitate, methyl stearate,
methyl oleate, methyl linoleate and methyl linolenate. The alcohol
can be selected from the group consisting of ethanol, propanol,
butanol, iso-amyl alcohol and mixtures thereof. The mixed fatty
acid esters are methyl and higher alcohol esters of palmitic acid,
stearic acid, oleic acid, linoleic acid and linolenic acid. The
fermentation derived organic acid can be selected from the group
consisting of lactic acid, succinic acid and mixtures thereof. In a
further exemplary embodiment, the organic acid can be selected from
the group consisting of propionic acid, butyric acid, isobutyric
acid, mixed carboxylic acids and mixtures thereof. These can be
used as additional fuel additives. In an exemplary embodiment, the
ether is dibutyl ether (DBE).
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a diagram illustrating the continuous process of
the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0026] All patents, patent applications, government publications,
government regulations, and literature references cited in this
specification are hereby incorporated herein by reference in their
entirety. In case of conflict, the present description, including
definitions, will control.
[0027] The present invention relates to (1) the preparation of
mixed esters of fatty acids and (2) mixtures of fatty acid methyl
esters and diethyl succinate/ethyl lactate (a succinic acid
ester/lactic acid ester), to be used as fuel in diesel engines. In
an exemplary embodiment, mixed esters of fatty acids and blended
FAME, a commercially available impure fatty acid methyl ester, have
cloud points 5-10.degree. C. lower than FAME (defined as Biodiesel
by National Biodiesel Board). The lower cloud points of these mixed
esters can make them more suitable than current biodiesel for use
as a diesel fuel, particularly without the use of chemical
additives. It is a further aspect of the present invention that the
exemplary mixed ester compositions can be blended in higher
concentrations into petroleum diesel than standard FAME.
[0028] It should be understood by those having skill in the art
that a fatty acid is generally described as a carboxylic acid
having an aliphatic tail (chain), either saturated or unsaturated
and typically unbranched. Carboxylic acids as short as butyric acid
(4 carbon atoms) are considered to be fatty acids. Fatty acids
derived from natural fats and oils usually have at least 8 carbon
atoms, e.g. caprylic acid (octanoic acid).
[0029] Most natural fatty acids have an even number of carbon
atoms, because their biosynthesis involves acetyl-CoA, a coenzyme
carrying a two-carbon-atom group. Fatty acids are typically
produced by the hydrolysis of the ester linkages in a fat or
biological oil (both of which are triglycerides), with the
production of glycerol. FAME (Fatty Acid Methyl Ester) is generally
characterized by the chemical formula, ROOCH3, wherein R is a fatty
acid carbon chain.
[0030] As used herein, the term "higher alkyl alcohols (ROH)"
refers to alcohols having 2 to 8 carbon atoms (e.g., as compared to
methanol). As used herein, a lower alkyl alcohol is an alcohol with
only one carbon such as methanol, but can be ethanol, propanol, or
butanol if reacted with a higher alkyl ester, wherein the alkyl has
more carbons than the alcohol (i.e., carbons of alkyl are greater
than carbons of alcohol). However, it is understood that the terms
"lower" and "higher" are relative terms based on the carbon atoms
of the alcohol and the alkyl group of the reacting ester. For
example, ethanol is a higher alkyl alcohol when reacted with a
lower-methyl-ester. In another example, butanol is a higher alkyl
alcohol when reacted with a lower-ethyl-ester.
[0031] Exemplary mixed esters according to the present invention
are synthesized using a transesterification process. The term
"transesterification" refers to a process of exchanging the lower
alkyl group of an ester compound with a higher alkyl group or vice
versa. These reactions are often catalyzed by the addition of an
acid or base.
Example
[0032] Higher alkyl Alcohol+lower alkyl ester.fwdarw.lower
alcohol+higher alkyl ester
[0033] Solid acid catalysts donate a proton to the carbonyl group,
thus making it more reactive.
[0034] The transesterification reactions associated in the Examples
below were carried out using several exemplary catalysts including
but not limited to: sodium ethylate (base), Amberlyst-15 (Bronsted
acid), Amberlyst-70 (acid), SBA-15/titanium diisoprpyl
bis(acac).sub.2, SBA-15 (acid), SBA-15/dibutyltin bis(acac).sub.2
(acid), SBA-15/aminopropyltrimethoxysilnae-titanium tetrachloride
(Lewis acid), SBA-15/ruthenium(acac).sub.2, and sulfated zirconia
(acid) catalysts. The sodium ethylate (NaOC2H5--also known as
sodium ethoxide) is a base that operates as a catalyst. Generally,
the base catalyst is not consumed in the reaction unless free fatty
acid is present. It is desirable to avoid the presence of free
fatty acid. Preferably the reaction mixture is substantially free
of free fatty acids. The presence of free fatty acids with the
sodium ethylate base catalyst forms a salt of the free acid. This
process is saponification and results in the formation of soap. In
an exemplary embodiment, the reaction mixture contains less than
1.0%-wt of free fatty acid, more preferably less than 0.1%-wt of
free fatty acid, and even more preferably less than 0.01%-wt of
free fatty acid. The term "acac" associated with the catalysts in
Experiment Nos. 8, 9, and 11 in Table 1 below refers to "acetyl
acetate", a common organic ligand used to make homogeneous
complexes of transition metals that are soluble in water. SBA-15 is
a mesoporous silica-alumina solid acid that serves as a catalyst
support for other oxide catalysts or as a catalyst itself. It is
related to zeolites in its composition and acidity. It is a common
material known in the art. Amberlyst 15 and Amberlyst 70 are strong
cationic exchange resins. Typically, Amberlyst 70 can tolerate
higher temperatures (150.degree. C. vs. 120.degree. C. for
Amberlyst 15), but at a cost of approximately 2/3 of the active
(acid) site concentration per unit mass. Sulfated zirconia is
ZrO.sub.2 that has been treated with sulfuric acid to produce
--SO.sub.3 groups on the surface. These are highly acid groups that
give sulfated zirconia its high catalyst activity. Typically, the
catalysts that are placed onto the SBA-15 support are
organometallic complexes of varying composition that are known to
be active acid catalysts. In an exemplary embodiment, FAME was used
as the starting substrate for reactions along with various
alcohols. Exemplary alcohols include but are not limited to:
ethanol, n-butanol, n-propanol and i-propanol among others.
[0035] In exemplary laboratory batch transesterification reactions,
FAME was mixed with at least one of the alcohols. FAME was also
used in a mixture of two or three alcohols and one of the
catalysts, mentioned hereinabove. In an exemplary embodiment, FAME
was a mixture of methyl palmitate, methyl stearate, methyl oleate,
methyl linoleate and methyl linolenate. The compositions are shown
as percent by weight: [0036] Methyl oleate: 25.9 [0037] Methyl
linoleate: 46.1 [0038] Methyl linolenate: 13.3 [0039] Methyl
palmitate: 5.4 [0040] Methyl stearate: 4.4 [0041] Monoglycerides:
3.24 [0042] Unknown: 1.66
[0043] For the monoglycerides, three different peaks were observed.
The value reported for monoglycerides was a combination of these
three peaks. This is typical of a soy or canola oil composition. In
an exemplary embodiment, unreacted alcohols from each reaction
mixture were removed by vacuum distillation and the final mixture,
containing only esters, was evaluated to determine the cloud point.
The results for various transesterification reactions involving
FAME as one of the reactants are reported with respect to Table 1.
The cloud point results for various ester mixtures are provided in
Table 2.
TABLE-US-00001 TABLE 1 Preliminary results for various
transesterification reactions % Re- Av- Exp. Temp. action erage No.
Alcohol MR Catalyst (.degree. C.) Time Conv* 1 Ethanol 6
Amberlyst-15 78 24 h 59 2 i-Propanol 6 Amberlyst-15 80 24 h 72 3
n-Propanol 6 Amberlyst-15 98 24 h 75 4 n-Butanol 6 Amberlyst-70 110
24 h 49 5 Ethanol 6 Sulfated zirconia 120 24 h 32 6 Ethanol 6
Amberlyst-15 120 24 h 65 7 Ethanol 6 No catalyst 120 24 h 5 8
Ethanol 6 SBA-15/ 120 24 h 22 Ti(acac).sub.2 (IPA).sub.2 9 Ethanol
6 SBA-15/ 120 24 h 44 (butyl).sub.2Sn(acac).sub.2 10 Ethanol 6
SBA-15 120 24 h 7 11 Ethanol 6 SBA-15/Ru(acac).sub.2 120 24 h 12 12
Ethanol 6 SBA-15/ 120 24 h 15 AMPTS-TiCl.sub.4 13 Ethanol 6
NaOC.sub.2H.sub.5 in 78 6 h 80 EtOH (21 wt %) 14 Ethanol 6
NaOC.sub.2H.sub.5 78 16 h 55 *The average of 5 major methyl-esters
of FAME reacted by transesterification reaction in a stirred batch
vessel. Experiment Nos. 1-4, 13, and 14 were performed at a
pressure of 1 atm. Experiment Nos. 5-12 were performed at
120.degree. C. and 60 psia, the vapor pressure of ethanol at that
temperature.
TABLE-US-00002 TABLE 2 Cloud point for mixed esters Mixtures Volume
Ratio Cloud point (.degree. C.) FAME 100:0 2 FAME + Ethyl lactate
90:10 -1 FAME + Ethyl lactate 70:30 -3 FAME + Diethyl succinate
90:10 -4 FAME + Diethyl succinate 70:30 -4 FAME + FAEE.sup.a 34:66
-5 FAME + FAIE.sup.b 27:73 -5 FAME + DBS.sup.c 90:10 -1 FAME + DBS
70:30 -3 FAME + FABE.sup.d 6:94 -4 FAME + FABE + DBS 5:85:10 -5
FAME + FABE + DBS 4:66:30 -7 FAME + FABE + DBS 3:47:50 -8 FAME +
FABE + DBS + DBE.sup.e 5:85:5:5 -4 FAME + FABE + DBS + DBE
4:66:20:10 -6 FAME + FABE + DBS + DBE 3:47:20:30 -11 FAME + FABE +
DBS + DBE 3:47:30:20 -12 FAME + FABE + DBS + DBE 3:47:40:10 -12
.sup.aFatty acid ethyl esters .sup.bFatty acid iso-propyl esters
.sup.cDibutyl succinate .sup.dFatty acid n-butyl ester
.sup.eDibutyl ether
[0044] Cloud point analysis, as in Table 2, of mixed alkyl esters
of fatty acids can range from about 5-14.degree. C. (9-25.degree.
F.) lower than methyl esters of fatty acids. Therefore, in an
exemplary embodiment these mixed esters can be used as diesel-fuel
in not-so-harsh winter conditions with few if not any further
additives. Since FAME is used as a substrate, the ratio of each
alkyl ester in the final mixture can be controlled by the extent of
conversion of methyl esters to respective alkyl ester or by
blending the pure FAME with other pure alkyl esters in various
proportions as per the requirements.
[0045] In the exemplary process associated with the present
invention, FAME was used as a substrate to synthesize fatty acids
ester of higher alcohol and solid acid catalysts instead of base
catalysts. Some of the advantages associated with these particular
exemplary processes include but are not limited to: [0046] 1) Use
of solid acid catalysts eliminates the problems associated with
base catalysts; and [0047] 2) The use of solid acid catalysts
allows the processes to be carried out on a continuous basis as
opposed to only batch processes, typical with base catalysts.
[0048] In an exemplary embodiment, the temperature at which the
reaction takes place with the acid catalysts is from about 50 to
200.degree. C. and the pressure can range from about 0.5 to 20
atmospheres. Operating conditions are largely dependent upon the
chosen catalyst. For example, ion exchange resins are typically
best up to 150.degree. C.
[0049] Fatty acid esters of other higher alcohols with 100%
conversion and 100% purity using FAME as a substrate are produced
on a continuous-scale by reactive distillation.
[0050] In a further aspect of the present invention the process of
synthesizing higher alkyl fatty acid esters from FAME via
transesterification with higher alcohols with solid acid catalysts,
was also a suitable method for converting residual triglycerides
(along with FAME in biodiesel) to alkyl esters of fatty acids. This
helps in maintaining the total glycerin concentration in the
biodiesel at a permissible level as per American Society for
Testing and Materials (ASTM) standard.
[0051] Thus, the present invention provides a process step in
biodiesel production that removes undesired impurities and provides
a mixed ester that inhibits crystal formation at lower temperature,
thus effectively eliminating the challenges associated with fuel
properties such as cloud point and therefore producing a
consistent, reliable diesel fuel substitute.
[0052] The process is shown in FIG. 1. The product stream from a
conventional biodiesel production facility contains primarily fatty
acid methyl esters (FAME) but contains small quantities of
impurities such as triglycerides (TG), diglycerides (DG),
monoglycerides (MG), glycerol (GO), methanol, water, and
transesterification catalyst. In conventional biodiesel production,
these impurities are removed (often incompletely) by a combination
of water washing and addition of solid absorbents. Both methods
lead to questionable results and generation of waste.
[0053] As shown in FIG. 1, in an exemplary process associated with
the present disclosure, a reactive distillation column is provided
as an add-on to existing biodiesel production plants to facilitate
purification of traditional biodiesel production. The
FAME+impurities stream is further transesterified with ethanol,
higher alcohols (C2 or higher) and/or a mixture thereof, in the
reactive distillation column. This process further transesterifies
the FAME and the Fatty Acid impurities thereby forming desired
product to be collected at the bottom of the column. The High
Purity biofuels contains mixed alkyl esters of fatty acids. The
impurities are essentially removed. In a further exemplary
embodiment, any glycerol present in the initial impure FAME stream
coming from the biodiesel process and feeding into the reactive
column is removed. Glycerol will leave the column at the bottom
along with the high purity mixed alkyl ester product stream.
Several techniques can be employed to essentially remove the
glycerol including but not limited to: a phase separation, washing
the biodiesel with water, or by using an adsorbent to remove
glycerol. U.S. Pat. No. 7,321,052 to Miller et al., the description
of which is incorporated by reference in its entirety herein,
describes a process for producing a glycerol acetal useful in
fuels. U.S. Pat. No. 6,548,681 to Chopade et al, the description of
which is incorporated by reference in its entirety herein,
describes the function and separation of polyol acetals, including
glycerol.
[0054] In the process diagram shown in FIG. 1, the biodiesel
product stream is fed to a reactive distillation column that
constitutes an important aspect of the present invention. The
reactive distillation column consists of a vertical vessel
containing a solid structural packing or a dumped packing in which
a catalyst material is held. The section of the column containing
the acid catalyst material is referred to as the reactive zone. In
an exemplary embodiment, the reaction zone comprises the catalyst
mounted in structured packing elements and supported as a single
unit of the structured packing elements. Liquid moves downward in
the column and vapors, generated via a reboiler at the base of the
column, move upward. In the reactive distillation column, the
biodiesel stream is fed near the top of the reactive zone and flows
downward over the catalyst. An alcohol such as ethanol or a mixture
of alcohols such as ethanol and butanol is added to the column near
the bottom of the reactive zone and flows upward as vapor over the
catalyst. In the catalyst zone, several reactions take place.
First, the unreacted mono-, di- and tri-glycerides (MG,DG,TG) are
transesterified with the alcohols to produce additional alkyl
esters of fatty acids and residual glycerol. This effectively
removes these impurities from the fuel stream. Second, a part of
the fatty acid methyl esters are transesterified to ethyl esters or
mixtures such as ethyl+butyl esters. This happens because there is
free alcohol in the column and because any methanol liberated in
transesterification enters the vapor phase and exits the top of the
distillation column. Third, depending on column temperature some
glycerol can undergo etherification with the alcohols present to
form glycerol ethers, which themselves are recognized fuel
components.
[0055] If all reactions take place appropriately, the product from
the bottom of the distillation column will be a small quantity of
glycerol and high purity mixed alcohol ester of fatty acids. This
mixture constitutes a biofuel with improved properties relative to
FAME from conventional biodiesel production. The biofuel leaving
the bottom of the column can be washed or treated with absorbent to
ensure purity to remove the residual glycerol, but most often that
will not be necessary. More likely, a simple phase separation step
to remove any unreacted residual glycerol will be carried out and
then the fuel can be sent to storage for use. The stream from the
top of the column consists of unreacted ethanol or mixed alcohol
feed, methanol liberated in transesterification or stripped from
the biodiesel. If the biodiesel contains water, then water also
leaves through the top of the column. Water is not per se generated
in the transesterification reaction. However, water can be formed
in biodiesel production if there are free fatty acids in the
starting triglyceride feedstock. Thus, water may be formed (via
etherification or esterification of free fatty acids) and is
subsequently removed through the top of the column with methanol
and any other residual alcohols. These alcohols can be recovered by
distillation and recycled into the process. The reaction kinetics
are favorable for the formation of the higher fatty acid esters, as
seen in Table 3.
TABLE-US-00003 TABLE 3 Rate constants for formation of ethyl, butyl
and isoamyl esters of fatty acids by transesterification of methyl
esters of fatty acids at various temperatures Temp (.degree. C.)
Rate constants; k (Kg.sub.sol.sup.2 .cndot. mol.sup.-1 .cndot.
Kg.sub.cat.sup.-1 .cndot. s.sup.-1) Ethyl oleate Butyl oleate
Isoamyl oleate 80 1.5 .times. 10.sup.-5 100 3 .times. 10.sup.-5 4
.times. 10.sup.-5 4 .times. 10.sup.-5 120 14 .times. 10.sup.-5 9
.times. 10.sup.-5 11 .times. 10.sup.-5 Ethyl linoleate Butyl
linoleate Isoamyl linoleate 80 1.5 .times. 10.sup.-5 100 3 .times.
10.sup.-5 4 .times. 10.sup.-5 4 .times. 10.sup.-5 120 14 .times.
10.sup.-5 9 .times. 10.sup.-5 11 .times. 10.sup.-5 Ethyl linolenate
Butyl linolenate Isoamyl linolenate 80 2.5 .times. 10.sup.-5 100
4.5 .times. 10.sup.-5 6 .times. 10.sup.-5 5.5 .times. 10.sup.-5 120
21.5 .times. 10.sup.-5 12.5 .times. 10.sup.-5 14.5 .times.
10.sup.-5
[0056] These rate constants are for the transesterification of
methyl esters to ethyl, butyl, or isoamyl esters as per the
following reaction: Fatty acid methyl ester+alcohol (e.g.
ethanol)=Fatty acid alkyl (ethyl)ester+methanol
[0057] The catalyst for these reactions is Amberlyst 15 cation
exchange resin. These results show that it is kinetically practical
to carry out transesterification of methyl esters to other esters
using ion exchange resins.
[0058] A set of experiments were conducted to characterize the
equilibrium constant for the transesterification of methyl esters
(e.g. biodiesel) to butyl or ethyl esters. The reactions were
carried out in stirred vessels in a laboratory, analogous to a
single equilibrium stage in a reactive distillation column, for
reaction times ranging from 2 hr to 8 days. Reactions were
considered to be at equilibrium when the composition was unchanged
over several sample collections. Table 4 shows the results of the
experiments using butanol and ethanol to make butyl esters and
ethyl esters of fatty acids. The data given in Table 4 show that a
single stage in a reactive distillation column can achieve
conversions of methyl ester to butyl ester of approximately 85%.
Accordingly, reactive distillation can be an effective and
efficient method to carry out the desired reactions. By changing
the ratio of alcohol to fatty acid methyl ester, mixed esters of
any desired composition via reactive distillation can be produced.
These mixed esters are useful as advanced biofuel components.
TABLE-US-00004 TABLE 4 Experimental results to measure
transesterification equilibrium constants. (Conditions: alcohol
with fatty acid methyl esters (FAMES) in 3:1 alcohol:FAME molar
ratio; 25 g FAMES in 75 ml Parr reactor, stir rate 1050 RPM.)
Catalyst Reaction Quantity Exp Temp (wt % Equilibrium No. Alcohol
(.degree. C.) Catalyst FAME) Conversion K.sub.eq 1 n-Butanol
100.000 Sulfuric acid 0.101 83.753 2.359 2 n-Butanol 100.000
Sulfuric acid 0.193 86.713 2.642 3 n-Butanol 100.000 Sulfuric acid
0.250 86.794 2.669 4 n-Butanol 120.000 Sulfuric acid 0.168 82.421
2.435 5 n-Butanol 130.000 Sulfuric acid 0.149 87.330 2.499 6
Ethanol 100.000 Amberlyst 15 5.000 83.190 1.965
[0059] The invention constitutes a low-cost, efficient approach to
producing a high-quality biofuel that meets fuel standards and has
improved fuel properties. The present invention provides for a
process for producing mixed esters of fatty acids as biofuel for
use in compression ignition (CI) engine, which comprises: (a)
partial transesterification of a mixture of fatty acid methyl
esters with at least one higher alcohol containing 2 to 8 carbon
atoms in the presence of a heterogeneous solid acid catalyst to
produce a mixture of the fatty acid methyl esters and higher
alcohol esters of the fatty acids; and (b) separating the catalyst
from the transesterified reaction mixture. Separation of the
alcohol esters of the fatty acids and the FAME can be accomplished
using traditional separation techniques such as distillation and/or
evaporation. The present invention further provides for a biofuel
composition for use in compression ignition (CI) engine which
comprises a mixture of fatty acid methyl esters and of fatty acid
esters of at least one alcohol containing 2 to 8 carbon atoms. The
cloud point of the mixture is lower in temperature than that of the
fatty acid methyl esters alone.
[0060] In an exemplary embodiment, the present invention provides
for a biofuel, for use in compression ignition (CI) engines,
comprising mixtures of fatty acid methyl esters, fatty acid esters
of at least one alcohol containing 2 to 8 carbon atoms, esters of a
fermentation derived organic acid with at least one alcohol
containing 1 to 6 carbon atoms and optionally an ether containing
at least 6 carbon atoms as an oxygenate. In an exemplary
embodiment, the fermentation derived organic acid can be derived
from a carbohydrate (such as sugar) fermentation source. Oxygenated
substances are typically described as those that have incorporated
oxygen in the molecule. The term "Oxygenates" typically refers to
fuels or additives containing oxygen. Oxygenates are usually
employed as additives to reduce carbon monoxide and carbon
particulates that are created during the burning of the fuel.
[0061] Oxygenates may be based on alcohols or ethers. Some
exemplary oxygenates in use include but are not limited to: [0062]
1) Alcohols: Methanol (MeOH); Ethanol (EtOH); Isopropyl alcohol
(IPA); n-butanol (BuOH); t-butanol; and [0063] 2) Ethers: Methyl
tert-butyl ether (MTBE); Tertiary amyl methyl ether (TAME);
Tertiary hexyl methyl ether (THEME); Ethyl tertiary butyl ether
(ETBE); Tertiary amyl ethyl ether (TAEE); propyl ether (DIPE);
Dipropyl ether; Dihexyl ether; Dioctyl ether, iso-amyl-ether.
[0064] Further exemplary oxygenate related compositions are
described in U.S. Pat. No. 6,468,319 issued to Yeh et al., the
subject matter of which is incorporated by reference in its
entirety herein. Yeh et al. describes diesel fuel containing ester
compositions effective in reducing emissions. U.S. Pat. No.
5,268,008 issued to Kanne describes hydrocarbon fuel compositions
containing orthoesters to reduce particulate emissions therefrom
when combusted in an internal combustion engine. Accordingly, the
description set forth in Kanne is incorporated by reference in its
entirety herein. The description of commonly owned U.S.
application, 2006/0014977, filed Jul. 19, 2004 is incorporated by
reference herein in its entirety.
[0065] While the present invention is described herein with
reference to illustrated embodiments, it should be understood that
the invention is not limited hereto. Those having ordinary skill in
the art and access to the teachings herein will recognize
additional modifications and embodiments within the scope thereof.
Therefore, the present invention is limited only by the claims
attached herein.
* * * * *