Title:
Microwave-enhanced process to maximize biodiesel production capacity
Kind Code:
A1


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, US)
Jensen, Scott (Kingwood, TX, US)
Application Number:
11/340137
Publication Date:
07/27/2006
Filing Date:
01/26/2006
Assignee:
Imperial Petroleum Recovery Corp. (Houston, TX, US)
Primary Class:
International Classes:
C10L5/00
View Patent Images:
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Primary Examiner:
WONG, EDNA
Attorney, Agent or Firm:
LOCKE LORD LLP (HOUSTON, TX, US)
Claims:
What is claimed is:

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° to about 60° 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° to about 60° 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° to about 60° 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° to about 60° 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

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

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

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° 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.

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 C1-C6 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.

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.

Thus, while transesterification is well known (and becoming increasingly important), there remains considerable inefficiencies in existing transesterification processes.

SUMMARY OF THE INVENTION

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.

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

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

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.

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.

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.

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.

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.

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.

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.

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° to about 90° 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).

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° Fahrenheit (F.).

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.

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° 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.

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° to about 60° F.

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.

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.

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.

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° to about 60° 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° to about 60° 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.

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.

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° to about 100° 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.

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° F.

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.

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

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.

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 1
(A)(B)(C)(D)
BrownGravityCentrifugeCentrifuge
GreaseSeparationSeparationSeparation
Feed(No MST)(No MST)(With MST)
FFA (w %)22.2512.1510.894.89
Sep'n Time (min)601201414
Products (v %)
Low FFA Oil213836364242
Emulsion483024242020
Water313240403838

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

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.

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 2
(B)(D)
(A)Gravity(C)Centrifuge
SoybeanSeparationCentrifugeSeparation
Oil Feed(NoSeparation(With
StockMST)(No MST)MST)
Total Glycerin (w %)Nil2.585.512.16
(Biodiesel phase)
Sep'n Time (min)2120.5120.512
Products (v %)
Biodiesel + Unreacted989296919285
Triglycerides
Glycerin/Methanol2849815
˜% Glycerin Recovered197729644889

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

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.

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 3
Gravity-based SettlingWater Content
Biodiesel ResolutionSep'n Time (min)in Biodiesel
(v % of Oil)0.51248(w %)
Without MST72849292960.3651
With MST8088961001000.3432
With MST1001001001001000.2158
(Std. Centrifuge)
Sep'n (Average
of two tests)

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)

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).

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 4
TotalGlycerin
CentrifugeGlycerinContent in
Sep'n Time (min)Prod'dBiodiesel
0.51248(v %)(v %)
Glycerin Yield (v %)
Without MST4688914.05.51
With MST81013151516.82.16
% of Final Glycerin
Produced
Without MST29435757100
With MST48597789100

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.

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.