U.S. patent application number 11/340137 was filed with the patent office on 2006-07-27 for microwave-enhanced process to maximize biodiesel production capacity.
This patent application is currently assigned to Imperial Petroleum Recovery Corp.. Invention is credited to Scott Jensen, Mark J. Porter.
Application Number | 20060162245 11/340137 |
Document ID | / |
Family ID | 36741089 |
Filed Date | 2006-07-27 |
United States Patent
Application |
20060162245 |
Kind Code |
A1 |
Porter; Mark J. ; et
al. |
July 27, 2006 |
Microwave-enhanced process to maximize biodiesel production
capacity
Abstract
An improved process for the production of biodiesel fuels and
fuel additives from triglyceride-containing feed stocks is
described wherein the improvement involves the use of microwave
energy to reduce free fatty acid content of feed stocks, enhance
the reaction rate and conversion yield of triglycerides to fatty
acid esters (biodiesel product), and/or assist in the separation of
at least one of the mixtures formed in the biodiesel production
process.
Inventors: |
Porter; Mark J.; (Crosby,
TX) ; Jensen; Scott; (Kingwood, TX) |
Correspondence
Address: |
JENKENS & GILCHRIST
1401 MCKINNEY
SUITE 2600
HOUSTON
TX
77010
US
|
Assignee: |
Imperial Petroleum Recovery
Corp.
Houston
TX
77032
|
Family ID: |
36741089 |
Appl. No.: |
11/340137 |
Filed: |
January 26, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60647332 |
Jan 26, 2005 |
|
|
|
Current U.S.
Class: |
44/605 |
Current CPC
Class: |
C10L 1/026 20130101;
C11C 3/003 20130101; Y02E 50/13 20130101; C11C 1/08 20130101; Y02E
50/10 20130101 |
Class at
Publication: |
044/605 |
International
Class: |
C10L 5/00 20060101
C10L005/00 |
Claims
1. In a method for making biodiesel fuel and fuel additive products
wherein a triglyceride-containing feed stock is reacted with an
alcohol in the presence of a transesterification catalyst to form a
first mixture of biodiesel product, alcohol and glycerin, the first
mixture subsequently undergoing a first separation for separating
the biodiesel product from unreacted alcohol and glycerin, the
biodiesel product subsequently undergoing a washing with a washing
agent to produce a second mixture of biodiesel product and washing
agent, the second mixture subsequently undergoing a second
separation for separating the biodiesel product from the washing
agent, the improvements comprising: directing radio frequency
microwave energy into at least one of: the first mixture prior to
the first separation for a time sufficient to reduce an amount of
unreacted alcohol and glycerin retained in the biodiesel product
and to reduce a time required for separating the biodiesel product
from the unreacted alcohol and glycerin; and the second mixture
prior to the second separation for a time sufficient to reduce an
amount of washing agent retained in the biodiesel product and to
reduce a time required for separating the biodiesel product from
the washing agent.
2. The method of claim 1 wherein the triglyceride-containing feed
stock includes vegetable oils, animal oils, and used cooking
oils.
3. The method of claim 1 wherein the radio frequency microwave
energy is directed into the first mixture for a time sufficient to
increase the temperature of the first mixture from about 5.degree.
to about 60.degree. Fahrenheit.
4. The method of claim 1 wherein the radio frequency microwave
energy is directed into the second mixture for a time sufficient to
increase the temperature of the second mixture from about 5.degree.
to about 60.degree. Fahrenheit.
5. The method of claim 1 wherein the flow rate of at least one of
the first mixture and the second mixture is from about 3 to about
120 gallons per minute.
6. The method of claim 1 wherein the washing agent is one of a
water-based washing agent and an acid-based washing agent.
7. The method of claim 1 wherein at least one of the first mixture
and the separation thereof and the second mixture and the
separation thereof occur in an integrated microwave separation
technology unit comprising both microwave application equipment and
phase separation equipment.
8. A method of enhancing a transesterification reaction rate and
biodiesel product yield for production of biodiesel fuel and fuel
additive products, comprising: reacting a triglyceride-containing
feed stock with an alcohol in the presence of a transesterification
catalyst to form a mixture of biodiesel product, alcohol, and
glycerin; applying radio frequency microwave energy to the mixture;
and separating the biodiesel product from unreacted alcohol and
glycerin; wherein the application of radio frequency microwave
energy is performed prior to the separating of biodiesel product to
increase the transesterification reaction rate and to drive a
reaction equilibrium toward biodiesel production to thereby
increase a yield of the biodiesel product available for recovery
from the unreacted alcohol and glycerin.
9. The method of claim 8 wherein the triglyceride-containing feed
stock includes vegetable oils, animal oils, and used cooking
oils.
10. The method of claim 8 wherein the radio frequency microwave
energy is applied to the mixture for a time sufficient to increase
the temperature of the mixture from about 5.degree. to about
60.degree. Fahrenheit.
11. The method of claim 8 wherein the applying of radio frequency
microwave energy to the mixture and the separating of the biodiesel
product are performed in an integrated microwave separation
technology unit comprising both microwave application equipment and
phase separation equipment.
12. The method of claim 8 wherein the flow rate of the mixture is
from about 3 to about 120 gallons per minute.
13. A method of reducing a free fatty acid content of
triglyceride-containing feed stocks used for production of
biodiesel fuel and fuel additive products, comprising: reacting a
triglyceride-containing feed stock having a first free fatty acid
content with a reactant to produce a treated mixture; applying
radio frequency microwave energy to the treated mixture to produce
a triglyceride-containing feed stock having a second free fatty
acid content, the second free fatty acid content being lower than
the first free fatty acid content; and separating the
triglyceride-containing feed stock having the second free fatty
acid content from a byproduct waste emulsion; wherein the
application of radio frequency microwave energy is performed prior
to the separating of triglyceride-containing feed stock for a time
sufficient to reduce an amount of free fatty acid retained in the
triglyceride-containing feed stock and to increase an amount of
triglyceride-containing feed stock having the second free fatty
acid content recovered from the byproduct waste emulsion.
14. The method of claim 13 wherein the first free fatty acid
content is greater than one percent by volume of the
triglyceride-containing feed stock.
15. The method of claim 13 wherein the triglyceride-containing feed
stock having the first free fatty acid content includes vegetable
oils, animal oils, and used cooking oils.
16. The method of claim 13 wherein the radio frequency microwave
energy is applied to the treated mixture for a time sufficient to
increase a temperature of the treated mixture from about 5.degree.
to about 60.degree. Fahrenheit.
17. The method of claim 13 wherein the applying of radio frequency
microwave energy to the treated mixture and the separating of the
triglyceride-containing feed stock are performed in an integrated
microwave separation technology unit comprising both microwave
application equipment and phase separation equipment.
18. The method of claim 13 wherein the flow rate of the mixture is
from about 3 to about 120 gallons per minute.
19. In a system for making biodiesel fuel and fuel additive
products wherein a triglyceride-containing feed stock is reacted
with an alcohol in the presence of a transesterification catalyst
to form a first mixture of biodiesel product, alcohol and glycerin,
the first mixture subsequently undergoing a first separation for
separating the biodiesel product from unreacted alcohol and
glycerin, the biodiesel product subsequently undergoing a washing
with a washing agent to produce a second mixture of biodiesel
product and washing agent, the second mixture subsequently
undergoing a second separation for separating the biodiesel product
from the washing agent, the improvements comprising: a microwave
separation technology unit configured to direct radio frequency
microwave energy into at least one of: the first mixture prior to
the first separation for a time sufficient to reduce an amount of
unreacted alcohol and glycerin retained in the biodiesel product,
and to reduce a time required for separating the biodiesel product
from the unreacted alcohol and glycerin; and the second mixture
prior to the second separation for a time sufficient to reduce an
amount of washing agent retained in the biodiesel product and to
reduce a time required for separating the biodiesel product from
the washing agent.
20. The system of claim 19 wherein the improvements further
comprise a microwave separation technology unit configured to
increase a transesterification reaction rate of the first mixture
and for driving a reaction equilibrium of the first mixture toward
biodiesel production to thereby increase a yield of the biodiesel
product available for recovery from the unreacted alcohol and
glycerin.
21. The system of claim 19 wherein the improvements further
comprise a microwave separation technology unit configured to
reduce an amount of free fatty acid in the triglyceride-containing
feed stock and for increasing an amount of triglyceride-containing
feed stock having the reduced amount of free fatty acid content
recovered.
22. The system of claim 19 wherein the microwave separation
technology unit configured to direct radio frequency microwave
energy into at least one of the first mixture and the second
mixture is combined with a phase separation device in a single
integrated unit.
23. The system of claim 20 wherein the microwave separation
technology unit configured to increase a transesterification
reaction rate is combined with a phase separation device in a
single integrated unit.
24. The system of claim 21 wherein the microwave separation
technology unit configured to reduce an amount of free fatty acid
is combined with a phase separation device in a single integrated
unit.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to, and hereby incorporates
by reference, U.S. Provisional Application No. 60/647,332 entitled
"Microwave-Enhanced Process to Maximize Biodiesel Production
Capacity," filed Jan. 26, 2005, with the United States Patent and
Trademark Office.
FIELD OF THE INVENTION
[0002] The present invention relates to an improved process for
preparing biodiesel fuels wherein the feed stock preparation,
reaction, and separation steps of the process are preceded by
directing of radio frequency microwave energy into the mixtures
prior to reacting and separating such mixtures to recover upgraded
feed stocks and biodiesel products.
BACKGROUND OF THE INVENTION
[0003] Transesterification of triglycerides is a reaction that has
been known for decades and has been practiced almost as long for
the production of biodiesel fuels and fuel additives. The reaction
uses feed stocks that contain triglycerides, such as various
vegetable oils, rapeseed oil, soy oil, and even waste animal fats
and cooking greases. In the case of waste fats and greases, the
feed stocks must typically be pretreated in order to lower their
free fatty acid (FFA) content. The processes described in the art
state an FFA limitation of less than 1% and carry out the reaction
at temperatures up to 100.degree. C. and pressures up to 10 bars.
For information regarding transesterification, the reader is
referred to U.S. Pat. Nos. 5,514,820, 5,578,090, and 6,174,501, for
example. Triglycerides and their compositions are similarly
described in U.S. Pat. No. 5,578,090, for example.
[0004] The processes used in the art for the production of
biodiesel fuels and fuel additives generally involve reacting a
triglyceride with an alcohol, particularly a lower alcohol such as
a C.sub.1-C.sub.6 alcohol, more particularly methanol or ethanol.
In the presence of a catalyst, for example, an alkaline catalyst
such as potassium hydroxide or sodium hydroxide, these processes
produce a fatty acid alkyl ester, glycerin, and unreacted alcohol
in the reaction mixture. As a result, separation is required, often
by settling, in order to remove the glycerin and the alcohol.
[0005] Settling is typically performed in a settling tank, with the
top phase of the reaction mixture being the biodiesel product. The
biodiesel product is thereafter recovered (e.g., decanted) from the
reaction mixture and is usually washed with water or an acid in
order to neutralize any remaining catalyst. A separation is again
required after the washing and is usually performed either in
another settling tank, a static separator, or a centrifuge.
Centrifuges are often used since separation in a static separator
is imprecise and often incomplete.
[0006] Thus, while transesterification is well known (and becoming
increasingly important), there remains considerable inefficiencies
in existing transesterification processes.
SUMMARY OF THE INVENTION
[0007] The present invention is an improvement over existing
transesterification processes generally described above and in the
prior art patents referred to previously. The improvement involves
applying radio frequency microwave energy to the reaction mixture,
including pre-preparation of suitable triglyceride-containing feed
stocks, prior to the reaction and/or the separation step. The
separation may then be performed using simple settling,
centrifuging, or any other suitable technique for separating
immiscible liquids. Application of radio frequency microwave energy
allows the use of high FFA content feed stocks, including animal
fats and used cooking oils, in existing transesterification
processes by promoting the removal of the fatty acid. Application
of radio frequency microwave energy also enhances the reaction rate
for the conversion of triglycerides to biodiesel, and also drives
the reaction equilibrium toward the production of biodiesel.
Application of radio frequency microwave energy further improves
product recovery in the separation of the biodiesel product from
alcohol and glycerin in the reaction mixture. Finally, application
of radio frequency microwave energy to the reaction mixture before
the separation of the wash water or acid solutions (used to remove
impurities from the biodiesel fuel or additive) helps speed up the
separation process and improves the yields.
[0008] Accordingly, directing radio frequency microwave energy into
the reaction mixture prior to at least one feed stock preparation,
reaction, or separation step of the transesterification process may
enhance the product yield and recovery, and directing radio
frequency microwave energy into the reaction mixture prior to each
feed stock preparation, reaction, and separation step may maximize
the product yield, recovery, and overall biodiesel production
capacity compared to a similar process without using radio
frequency microwave energy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 and FIG. 2 are schematic flow sheets showing an
arrangement of various elements and steps of the
transesterification process according to embodiments of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0010] Biodiesel fuel or fuel additive is produced by subjecting a
suitable triglyceride-containing feed stock (e.g., soy oil, virgin
vegetable oil, used cooking oils, animal oils and other suitable
triglyceride-containing feed stocks) to known transesterification
or methyl- or ethyl-esterification processes. The processes result
in an effluent stream of esterified triglycerides, also referred to
as fatty acid esters, or esterified biodiesel product, and crude
glycerol, where glycerol is a term that refers to a mixture of
glycerin reaction byproduct and unreacted alcohol.
[0011] Production capacity for producing biodiesel can be limited
by separation processes because the crude glycerol is inherently
insoluble in the esterified biodiesel product. Furthermore, the
biodiesel is often washed with water (or an acid) to neutralize
residual catalysts and remove impurities, forming a biodiesel/water
emulsion. Gravity separation of the crude glycerol from the
biodiesel and subsequently the biodiesel from the wash water causes
the process to function as a semi-batch process, which constrains
use of other process equipment and limits throughput for the entire
system.
[0012] Production yields of biodiesel can also be constrained by
the reaction rate for converting triglycerides to the esterifed
biodiesel product, and by the reaction equilibrium that constrains
how much of the triglyceride will be converted to esterified
biodiesel product.
[0013] Furthermore, while a wide range of triglyceride-containing
feed stocks can be used for the transesterification process, feeds
that contain high levels of free fatty acids (FFA more than about 1
w %) are particularly desirable because of their low cost and
availability. These feed stocks have heretofore been technically or
economically undesirable, however, because the high FFA content
inhibits the transesterification reaction and forms inseparable
mixtures when treated by known methods for reducing the FFA
content.
[0014] Embodiments of the invention provide a way to mitigate or
overcome the above limitations by applying radio frequency
microwave energy to the feed stocks, reactants, or product mixtures
to be separated. The unique characteristics of radio frequency
microwave energy--specifically, the establishment of rapidly
oscillating electric and magnetic fields that selectively energize
strongly polar and strongly charged molecules relative to non-polar
and neutral, or less polar and less charged, molecules--allow
microwaves to facilitate certain physical and/or chemical reactions
that are favorable to the biodiesel production process.
[0015] Embodiments of the invention take advantage of the
above-mentioned unique characteristics of radio frequency microwave
energy to improve the biodiesel production process. For example, in
some embodiments, the radio frequency microwave energy may be used
to reduce the FFA content of high FFA triglyceride-containing feed
stocks, such as animal fats and used cooking oils, by enhancing the
conversion of free fatty acids and by enhancing the separation of
the lower FFA triglyceride-containing feed stock from the treatment
byproducts. In other embodiments, radio frequency microwave energy
may be used to enhance the rate of the transesterification reaction
and the yield of biodiesel product. The radio frequency microwave
energy helps drive the reaction to completion and facilitates
separation of glycerin and unreacted alcohol (or glycerol) from
other reaction products and intermediates, primarily biodiesel
product composed of a blend of fatty acid esters and trace
impurities. In still other embodiments, the radio frequency
microwave energy may also be used to facilitate separation of both
the biodiesel product from the glycerin byproduct and unreacted
alcohol, and the biodiesel product from wash water or other washing
agents that are used to neutralize and remove the trace impurities
and any residual catalysts. Embodiments of the invention also
provide a novel process and hardware for achieving the above
benefits.
[0016] The terms "microwave" and "radio frequency microwave
energy," as used herein, refer to energy having a wavelength in the
range of about 0.005 to 0.5 meters, although those having ordinary
skill in the art will understand that higher or lower wavelength
energy may also be used without departing from the scope of the
invention. In addition, while a number of specific values and
ranges are disclosed herein for temperature, residence time, flow
rate, weight percentage, volume percentage, ratio, and so forth,
those having ordinary skill in the art will recognize that other
values and ranges may also be used without departing from the scope
of the invention.
[0017] FIG. 1 shows a flow sheet 100 for a processing plant for
operating a methyl-esterification process according to one
embodiment of the invention. As can be seen, the
triglyceride-containing feed stock is delivered from a raw feed
tank 102 and mixed intensively with methanol and catalyst from a
mix tank 104. The reaction may take place in one or more mixers
106, such as one or more static mixers, tube reactors, one or more
heated, continuously stirred tank reactors, and the like. In some
embodiments, the reaction may occur at a temperature from about
20.degree. to about 90.degree. Celsius (C.) and a pressure from
about 1 to about 200 atmospheres. The mole ratio of methanol to
triglyceride-containing feed stock may be from about 1:1 to about
10:1. The flow rate of the reaction mixture may be from about 3 to
about 120 gallons per minute (gpm).
[0018] The reaction mixture then enters a microwave separation
technology (MST) unit 108 where radio frequency microwave energy is
applied to the reaction mixture. Application of radio frequency
microwave energy drives the reaction rate higher and drives the
reaction equilibrium toward higher production of transesterified
biodiesel product. Any suitable MST may be used for the
reaction-driving MST unit 108, including the MST shown and
described in U.S. Pat. Nos. 5,914,014; 6,077,400; and 6,086,830,
which patents are hereby incorporated by reference. In one
embodiment, the residence time in the reaction-driving MST unit 108
may be from about 0.2 to about 2 minutes, which should be
sufficient to increase the temperature of the reaction mixture by
about 50 to about 60.degree. Fahrenheit (F.).
[0019] From the reaction-driving MST unit 108, the reaction mixture
may optionally proceed to a reaction mixture separation device 110.
The reaction mixture separation device 110, which may be any
suitable separation device known to those having ordinary skill in
the art, separates the reaction mixture into its constituent
phases, glycerin plus unreacted alcohol, referred to as glycerol,
and biodiesel product. Glycerol is the lower phase and is
thereafter transferred to a glycerol methanol recovery unit 112.
The glycerol methanol recovery unit 112 separates the glycerol into
glycerin and methanol and recycles the methanol for use in catalyst
mix tank 104. In some embodiments, however, it may not be desirable
to recycle the methanol, depending on the particulars of the
application. Indeed, in some embodiments, ethanol, propanol or any
carbon chain length alcohol may be used instead of methanol.
[0020] Biodiesel product, which is the upper phase, is then mixed
with wash water from a wash water tank 114 (and is sometimes acid
neutralized) to produce a biodiesel product/wash water mixture.
Mixing may be performed in one or more mixers 116, such as one or
more static mixers, one or more heated, continuously stirred tank
reactors, and the like. The mixing may occur at a temperature from
about 15 to about 80.degree. C. and a pressure from about 1 to
about 5 atmospheres. The flow rate of the biodiesel product/wash
water mixture may be from about 3 to about 120 gallons per
minute.
[0021] The biodiesel product/wash water mixture is then transferred
to another MST unit 118 where radio frequency microwave energy is
applied to the mixture. Application of radio frequency microwave
energy at this point assists in the subsequent separation of the
biodiesel product/wash water mixture into its constituent phases,
water and biodiesel product. The lower phase water may then be
recycled to the wash water tank 114, while the upper phase
biodiesel product may be recovered. In some embodiments, the
water-washing MST unit 118 may be of a type similar to the
reaction-driving MST unit 108, although any suitable MST may be
used without departing from the scope of the invention. The
residence time in the water-washing MST 118 may be from about 0.2
to about 2 minutes, resulting in a temperature increase of the
mixture by about 5.degree. to about 60.degree. F.
[0022] In some embodiments, one or more reactor units (not
expressly shown) and/or one or more additional MST units may be
inserted into the process shown in FIG. 1 to further drive the
transesterification reaction and/or improve the separation of the
biodiesel product. For example, a reactor unit may be inserted into
the process of FIG. 1 between the mixer 106 and the
reaction-driving MST unit 108 to provide additional reaction time
before separating the biodiesel product from the glycerin. The
reactor unit may be any suitable reactor unit known to those having
ordinary skill in the art, including one or more static mixers,
tube reactors, one or more heated, continuously stirred tank
reactors, and the like. Alternatively, the reactor unit may be
inserted into the process between the reaction-driving MST unit 108
and the reaction mixture separation device 110 to help drive the
transesterification reaction. For this configuration, is also
possible to insert another MST unit between the reactor unit and
the reaction mixture separation device 110 in order to both drive
the reaction and improve the separation. These configurations and
other similar configurations that serve to enhance the reaction
rate and product yield and to facilitate separation of the
resulting product mixture may be used without departing from the
scope of the invention.
[0023] In accordance with the above-referenced U.S. Pat. Nos.
5,914,014; 6,077,400; and 6,086,830, the reaction-driving MST unit
108 and the water-washing MST unit 118 may include a radio
frequency microwave energy applicator. The radio frequency
microwave energy applicator may be used to direct radio frequency
microwave energy into a chamber through which the mixture to be
treated (i.e., high FFA feed stock, reaction mixture,
biodiesel/glycerin mixture, or biodiesel/wash water mixture)
passes. The radio frequency microwave energy is preferably
reflected into one or more radio frequency terminal cavities, for
example, by means of angled reflector plates located at the
terminal end of a rectangular waveguide. The waveguide terminal
reflector plates are sized and angled to minimize radio frequency
losses and to prevent reflected energy from returning to and
damaging the radio frequency transmitter. Low loss, radio
frequency-transparent, flat plate windows may be used to prevent
intrusion of the mixture into the waveguide.
[0024] The mixture to be treated is then flowed through the
chamber, preferably upward against gravity to prevent entrained
solids from becoming trapped within the applicator cavities. The
reentrant chamber dimensions may closely match the microwave
standing wave patterns, based on the dielectric nature of the feed
mixture flowing through the chamber. A three port circulator may be
placed within the transmission path between the transmitter and the
radio frequency microwave applicator to divert any reflected radio
frequency microwave energy to a water-cooled dummy load.
[0025] The inlet and outlet temperatures of the reaction-driving
MST unit 108 and the water-washing MST unit 118 are monitored and
the flow rate of the feed stock is controlled to maintain optimal
residence times and exit temperatures. This helps ensure an optimum
reaction performance and separation of the mixture components. An
optimum temperature differential of the feed stock between the
inlets and outlets of the microwave chamber may be fed back to the
pump feed rate controller. Pumping rate may then be changed to
maintain the proper temperature difference for optimum treatment.
In some embodiments, the temperature differential of the
reaction-driving MST unit 108 between the inlets and outlets of the
microwave chamber is from about 5.degree. to about 60.degree. F. In
some embodiments, the temperature differential of the water-washing
MST unit 118 between the inlets and outlets of the microwave
cavities is preferably from about 5.degree. to about 60.degree. F.
Those having ordinary skill in the art may of course adjust the
mixture flow rate or the intensity of the radio frequency microwave
energy as needed to obtain the optimum operating parameters for
each specific process.
[0026] In some embodiments, one or both of the MST units 108 and
118 may comprise a stand-alone microwave application system that is
separate from the separation devices 110 and 120. In other
embodiments, however, one or both of the MST units 108 and 118 may
be a microwave application system that also includes a separation
device. The separation device may be any suitable separation device
known to those having ordinary skill in the art, including gravity
or mechanically enhanced devices (e.g., centrifuge, hydrocyclone,
tank, etc.), or other commercially available separation devices. It
is believed that the techniques for combining the MST and
separation device into a single unit are well within the knowledge
of those having ordinary skill in the art and is therefore not
described here. Application of the MST units 108 and 118, whether
alone or in combination with a separation device, helps make it
possible to operate many biodiesel production plants in a
continuous operation that can significantly enhance biodiesel
production capacity.
[0027] FIG. 2 shows a flow sheet 200 according to some embodiments
of the invention where radio frequency microwave energy is used to
enhance the reduction of free fatty acids in high FFA
triglyceride-containing feed stocks, thereby making these feed
stocks more suitable for biodiesel production. As can be seen, the
high FFA triglyceride-containing feed stock is delivered from a raw
feed tank 202 and mixed intensively with a carbonate or bicarbonate
or other suitable reactant from a mix tank 204. The reaction may
take place in one or more mixers 206, such as one or more static
mixers, tube reactors, one or more heated, continuously stirred
tank reactors, and the like. In some embodiments, the reaction may
occur at a temperature from about 20.degree. to about 100.degree.
C. and a pressure from about 1 to about 100 atmospheres. The volume
ratio of reactant to high FFA triglyceride-containing feed stock
may be from about 0.1:1 to about 10:1. The flow rate of the
reaction mixture may be from about 3 to about 120 gallons per
minute.
[0028] The high FFA reaction mixture then enters an MST unit 208
where radio frequency microwave energy is applied to the high FFA
reaction mixture. Application of radio frequency microwave energy
drives the reduction in FFA and enhances the separability of the
resulting lower FFA triglyceride-containing feed stock and the
byproduct waste emulsion. Any suitable MST may be used for the
FFA-reducing MST unit 208, including the MST shown and described in
U.S. Pat. Nos. 5,914,014; 6,077,400; and 6,086,830 (incorporated
previously by reference). In one embodiment, the residence time in
the FFA reducing MST unit 208 may be from about 0.2 to about 2
minutes, which should be sufficient to increase the temperature of
the reaction mixture by about 50 to about 60.degree. F.
[0029] From the FFA-reducing MST unit 208, the reduced FFA reaction
mixture may optionally proceed to a reaction mixture separation
device 210. The reduced FFA reaction mixture separation device 210,
which may be any suitable separation device known to those having
ordinary skill in the art, separates the reduced FFA reaction
mixture into its constituent phases, a lower FFA
triglyceride-containing feed stock, and a resulting byproduct waste
emulsion. The byproduct waste emulsion is the lower phase and is
thereafter transferred to a waste handling or disposal unit 212.
The lower FFA triglyceride-containing feed stock is transferred to
a feed tank 214 for conversion into biodiesel.
[0030] Various embodiments of the invention may be better
understood by reference to the following examples.
EXAMPLE 1
Use of Radio Frequency Microwave Energy to Upgrade High Free Fatty
Acid Biodiesel Feeds
[0031] Many processes for production of biodiesel fuels rely on the
use of natural or food-grade oils (e.g., soybean, corn or palm oil)
as feed stocks. It is often desirable to use lower quality, lower
cost, waste oil feed stocks (e.g., waste cooking oils classified as
yellow or brown grease, or animal fats), but such feed stocks are
typically characterized by high FFA content (e.g., up to 40 w % or
more). The high FFA inhibits the processing characteristics of
these feed stocks due to the formation of water and soap that, in
turn, inhibit the reaction of triglycerides to ester products and
the separation of glycerin intermediates from the biodiesel
product.
[0032] In Example 1, a waste cooking oil brown grease was treated
using a well-known bicarbonate-based procedure for reducing FFA
content of high FFA feeds. A portion of the sample was then treated
using radio frequency microwave energy applied using MST as
described above. Samples not treated with MST were then separated
using well-known gravity separation and centrifuge separation
procedures. The MST treated samples were likewise separated using a
well-known laboratory centrifuge procedure. TABLE-US-00001 TABLE 1
(A) (B) (C) (D) Brown Gravity Centrifuge Centrifuge Grease
Separation Separation Separation Feed (No MST) (No MST) (With MST)
FFA (w %) 22.25 12.15 10.89 4.89 Sep'n Time (min) 60 120 1 4 1 4
Products (v %) Low FFA Oil 21 38 36 36 42 42 Emulsion 48 30 24 24
20 20 Water 31 32 40 40 38 38
[0033] As can be seen from Table 1, MST-enhanced FFA treating
(column D) significantly enhances the reduction in feed stock FFA
content relative to conventional FFA treating without MST (columns
B and C) for brown grease feed stock (column A). The feed stock
undergoing MST-enhanced FFA reduction treatment showed
significantly increased low FFA oil yield and/or rate of separation
of emulsion and water byproducts from the low FFA oil (42% oil
after 1 minute) relative to either the conventional gravity-based
process without MST (21% oil after 60 minutes or 38% oil after 120
minutes) or the centrifuge process without MST (36% oil after 1
minute).
EXAMPLE 2
Use of Radio Frequency Microwave Energy to Facilitate
Biodiesel/Glycerin Separation
[0034] The reaction of an oil triglyceride feed stock with methanol
forms a mixture of fatty acid esters (biodiesel product) in which
glycerin is generated as the major byproduct. Example 2 illustrates
an improvement in the separation of the biodiesel product and the
glycerin when the mixture is treated with radio frequency microwave
energy as described above.
[0035] In Example 2, a soybean oil feed was treated with a
well-known homogeneous catalyst prepared from methanol and
potassium hydroxide (KOH) to produce biodiesel. A portion of the
sample was also treated with MST. Samples not treated with MST were
then separated using well-known gravity settling and laboratory
centrifuge separation procedures. The MST-treated sample was
similarly separated using a well-known centrifuge procedure.
TABLE-US-00002 TABLE 2 (B) (D) (A) Gravity (C) Centrifuge Soybean
Separation Centrifuge Separation Oil Feed (No Separation (With
Stock MST) (No MST) MST) Total Glycerin (w %) Nil 2.58 5.51 2.16
(Biodiesel phase) Sep'n Time (min) 2 12 0.5 12 0.5 12 Products (v
%) Biodiesel + Unreacted 98 92 96 91 92 85 Triglycerides
Glycerin/Methanol 2 8 4 9 8 15 .about.% Glycerin Recovered 19 77 29
64 48 89
[0036] As can be seen from Table 2, the results indicate: 1)
MST-treated biodiesel/glycerin separation (column D) enhances the
removal of glycerin from the biodiesel product phase relative to
conventional separation without MST (columns B and C), and 2)
MST-treated biodiesel/glycerin separation increases the rate and
absolute percentage recovery of glycerin from the biodiesel (48%
after 0.5 minutes and 89% after 12 minutes) relative to either the
conventional gravity-based separation without MST (19% after 2
minutes and 77% after 12 minutes) or centrifuge-based separation
without MST (29% after 0.5 minutes and 64% after 12 minutes).
EXAMPLE 3
Use of Radio Frequency Microwave Energy to Facilitate
Biodiesel/Water and Acid Wash Separation
[0037] Following the conversion of triglycerides to fatty acid
esters (biodiesel product) and the subsequent separation of
biodiesel product from glycerin and residual methanol catalyst, it
is generally necessary to water wash, and sometimes acid
neutralize, the biodiesel product before it can be considered a
finished product. The water wash--and more commonly, the acid
wash--results in formation of emulsions that need to be separated.
Microwave enhancement is beneficial where an acid wash has been
conducted as well as on the sample washed with water as described
below.
[0038] In Example 3, a soybean oil feed was treated with a standard
homogeneous catalyst prepared from methanol and KOH to produce
biodiesel. The resulting biodiesel product and glycerin phases were
separated using a well-known gravity-based separation procedure.
The biodiesel product was then water washed using a 50/50
volumetric ratio of biodiesel and water using an in-line static
mixer to insure complete mixing. A portion of the sample was also
treated using radio frequency microwave energy applied by MST
immediately downstream of the static mixer. Samples not treated
with MST were then separated using a well-known gravity-based
separation procedure. The MST-treated sample was separated using
the same gravity-based separation procedure and also a well-known
centrifuge separation procedure to simulate operation in a typical
commercial MST configuration. TABLE-US-00003 TABLE 3 Gravity-based
Settling Water Content Biodiesel Resolution Sep'n Time (min) in
Biodiesel (v % of Oil) 0.5 1 2 4 8 (w %) Without MST 72 84 92 92 96
0.3651 With MST 80 88 96 100 100 0.3432 With MST 100 100 100 100
100 0.2158 (Std. Centrifuge) Sep'n (Average of two tests)
[0039] As can be seen from Table 3, the results indicate: 1)
MST-enhanced biodiesel product/wash water separation recovers a
biodiesel product more quickly than a conventional separation
without MST, 2) MST-enhanced biodiesel product/wash water
separation reduces the amount of water retained in the separated
biodiesel product, and 3) use of microwave energy in a well-known
commercial configuration that includes a centrifuge separator
increases the rate of biodiesel product/wash water separation and
reduces the amount of water retained in the biodiesel phase.
EXAMPLE 4
Use of MST Hardware as a Method to Commercially Achieve
Microwave-Enhanced Benefits on the Reaction of Triglycerides to
Fatty Acid Esters (Biodiesel)
[0040] Processes for production of biodiesel fuels are well known
and are becoming increasingly common in commercial practice. The
key reaction that characterizes biodiesel production involves
conversion of an oil triglyceride feed stock into-a mixture of
fatty acid esters (biodiesel product). Microwave heating increases
the reaction rate for converting triglycerides to fatty acid esters
(biodiesel product), and drives the ultimate reaction equilibrium
toward the production of fatty acid esters (biodiesel product).
[0041] In Example 4, a soybean oil feed was treated with a standard
homogeneous catalyst prepared from methanol and KOH to produce
biodiesel product. A portion of the sample was also treated with
microwave energy from an MST unit. Samples were then separated
using a well-known centrifuge separation procedure. The volume of
glycerin formed by the reaction and separated by the centrifuge
separation procedure was recorded at centrifuge times from about
0.5 to about 8 minutes and the glycerin yield at each time was
calculated as a percentage of the total final volume of glycerin
produced. TABLE-US-00004 TABLE 4 Total Glycerin Centrifuge Glycerin
Content in Sep'n Time (min) Prod'd Biodiesel 0.5 1 2 4 8 (v %) (v
%) Glycerin Yield (v %) Without MST 4 6 8 8 9 14.0 5.51 With MST 8
10 13 15 15 16.8 2.16 % of Final Glycerin Produced Without MST 29
43 57 57 100 With MST 48 59 77 89 100
[0042] As can be seen from Table 4, the results indicate: 1)
MST-enhanced biodiesel production yielded a higher final total
volume of glycerin (16.8 v %) than production without MST (14.0 v
%), where glycerin yield is directly proportional to and indicative
of a higher yield of fatty acid ester (biodiesel product), and 2)
MST-enhanced biodiesel production increased the reaction rate at
which biodiesel was produced relative to production without MST, as
indicated by the more rapid percentage production of glycerin and
higher final yield, which is also directly proportional to and
indicative of a higher rate and volume of biodiesel production.
[0043] While the present invention has been described with
reference to one or more particular embodiments, those skilled in
the art will recognize that many changes may be made thereto
without departing from the spirit and scope of the invention.
Therefore, each of the foregoing embodiments and obvious variations
thereof is contemplated as falling within the spirit and scope of
the claimed invention, which is set forth in the following
claims.
* * * * *