U.S. patent application number 12/557602 was filed with the patent office on 2010-08-26 for method for purifying biodiesel fuel.
This patent application is currently assigned to USA as represented by the Administrator of the National Aeronautics and Space Administration. Invention is credited to Tarek Abdel-Fattah, Anmar Lou J. Siochi, Antonio C. Siochi, Emilie J. Siochi, William T. Yost.
Application Number | 20100212219 12/557602 |
Document ID | / |
Family ID | 42629655 |
Filed Date | 2010-08-26 |
United States Patent
Application |
20100212219 |
Kind Code |
A1 |
Siochi; Emilie J. ; et
al. |
August 26, 2010 |
Method for Purifying Biodiesel Fuel
Abstract
A method for purifying a biodiesel fuel includes the use of
subjecting a biodiesel fuel to an electric field. The electric
field forms a precipitate in the fuel that removes the impurities
of excess catalysts and soap that are byproducts of the reaction
that forms the biodiesel. This electric field assisted washing
process can be applied to a biodiesel fuel in a batch process or,
alternatively, in a continuous process.
Inventors: |
Siochi; Emilie J.; (Newport
News, VA) ; Siochi; Anmar Lou J.; (Newport News,
VA) ; Yost; William T.; (Newport News, VA) ;
Siochi; Antonio C.; (Newport News, VA) ;
Abdel-Fattah; Tarek; (Yorktown, VA) |
Correspondence
Address: |
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION;LANGLEY RESEARCH CENTER
MAIL STOP 141
HAMPTON
VA
23681-2199
US
|
Assignee: |
USA as represented by the
Administrator of the National Aeronautics and Space
Administration
Washington
DC
|
Family ID: |
42629655 |
Appl. No.: |
12/557602 |
Filed: |
September 11, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61099654 |
Sep 24, 2008 |
|
|
|
Current U.S.
Class: |
44/388 |
Current CPC
Class: |
Y02E 50/10 20130101;
C10L 1/19 20130101; C11C 1/08 20130101; Y02E 50/13 20130101; C10L
1/026 20130101; C11C 3/003 20130101 |
Class at
Publication: |
44/388 |
International
Class: |
C10L 1/18 20060101
C10L001/18 |
Goverment Interests
ORIGIN OF THE INVENTION
[0002] The invention was made in part by employees of the United
States Government and may be manufactured and used by or for the
Government of the United States of America for governmental
purposes without the payment of any royalties thereon or therefor.
Claims
1. A method for purifying a biodiesel fuel comprising the steps of:
providing a triglyceride, methanol, and homogeneous catalyst;
reacting a mixture of the triglyceride, methanol and catalyst to
form a reaction product comprising a glycerol fraction and a crude
biodiesel fuel fraction; separating the glycerol and crude
biodiesel fuel fractions; subjecting the biodiesel fuel fraction to
an electric field to form a precipitate in the crude biodiesel fuel
fraction; and removing the precipitate from the remaining biodiesel
fuel fraction; whereby the remaining biodiesel fuel fraction after
removal of the precipitate is more purified than the crude
fraction.
2. A method for purifying a biodiesel fuel as described in claim 1,
wherein the triglyceride is selected from the group consisting of
triglycerides with long chain carbon and hydrogen atoms consisting
of 11 to 18 carbon atoms, vegetable oil, soybean oil, corn oil,
rapeseed oil, canola oil, peanut oil, cottonseed oil, safflower
oil, linseed oil, coconut oil, animal fat, lard, tallow and
mixtures thereof.
3. A method for purifying a biodiesel fuel as described in claim 1,
wherein the homogeneous catalyst is selected from the group
consisting of sodium hydroxide, potassium hydroxide, and sodium
methoxide.
4. A method for purifying a biodiesel fuel as described in claim 1,
wherein the crude biodiesel fuel fraction comprises methyl
esters.
5. A method for purifying a biodiesel fuel as described in claim 1,
wherein the step of subjecting the crude biodiesel fraction to an
electric field is performed in a batch process.
6. A method for purifying a biodiesel fuel as described in claim 1,
wherein the step of subjecting the crude biodiesel fraction to an
electric field is performed in a continuous process.
7. A method for purifying a biodiesel fuel as described in claim 1,
wherein the electric field has a strength of at least about 20
V/cm.
8. A method for purifying a biodiesel fuel as described in claim 1,
wherein the electric field has a strength in the range of about 10
to 200 V/cm.
9. A method of purifying a crude biodiesel fuel comprising the
steps of providing a crude biodiesel fuel formed by a process
comprising homogeneous catalysis; placing the crude biodiesel fuel
in an electric field to form a precipitate; removing the
precipitate from the crude biodiesel fuel.
10. A method for purifying a biodiesel fuel as described in claim
9, wherein the crude biodiesel fuel fraction comprises methyl
esters.
11. A method for purifying a biodiesel fuel as described in claim
9, wherein the step of subjecting the crude biodiesel fraction to
an electric field is performed in a batch process.
12. A method for purifying a biodiesel fuel as described in claim
9, wherein the step of subjecting the crude biodiesel fraction to
an electric field is performed in a continuous process.
13. A method for purifying a biodiesel fuel as described in claim
9, wherein the electric field has a strength of at least about 20
V/cm.
14. A method for purifying a biodiesel fuel as described in claim
9, wherein the electric field has a strength in the range of about
10 and 200 V/cm.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/099,654, filed Sep. 24, 2008, entitled "An
Electric Field Assisted Method for Biodiesel Purification".
BACKGROUND
[0003] The present invention is directed to the use of an electric
field for biodiesel fuel purification during the manufacture of
biodiesel fuel.
[0004] Biodiesel fuel is commercially produced by homogeneous
catalysis of transesterification from oil to methyl esters. The
homogeneous production method has some commercial inefficiencies in
it. One of the most expensive parts of the homogeneous biodiesel
production process is the washing step. Crude biodiesel is washed
with distilled water once it has been transesterified in order to
remove excess catalyst and soap. This is a critical step in the
production process because the leftover catalyst, generally sodium
hydroxide, may induce clogging or have caustic effects upon the
engine. Distilled water, however, is expensive and is used
profusely during the washing process. Apart from the extensive use
of distilled water, the catalyst cannot be recovered once it has
been used to facilitate the reason.
[0005] The biodiesel research community has looked into
heterogeneous catalysis as an alternative, anticipating that it
will be cheaper and faster than the current homogeneous process.
Currently however, it is more viable to use the homogeneous
catalysis method since it takes less time. Due to existing
infrastructure, many companies will be unwilling to dramatically
change their process. Sodium hydroxide, the preferred catalyst used
in commercial plants, is also fairly cheap, easy to access, and
produces a high conversion rate, making it the ideal catalyst to
use.
SUMMARY
[0006] Accordingly, it is an object of the present invention to
facilitate the washing of biodiesel fuel during the synthesis of
that fuel. Specifically, the biodiesel fuel is subjected to an
electric field that will precipitate out unwanted byproducts of the
synthesis reaction that formed the biodiesel fuel.
[0007] In one example, a method for purifying a biodiesel fuel
comprises the steps of providing a triglyceride, methanol, and
homogeneous catalyst. A mixture of the triglyceride, methanol, and
catalyst is reacted to form a reaction product comprising a
glycerol fraction and a crude biodiesel fuel fraction. The glycerol
and crude biodiesel fuel fractions are separated. The biodiesel
fuel fraction is subjected to an electric field to form a
precipitate in the crude biodiesel fuel fraction. The precipitate
is then removed from the biodiesel fuel fraction, whereby the
remaining biodiesel fuel fraction after removal of the precipitate
is more purified than the crude fraction.
[0008] In another example, a method of purifying crude biodiesel
fuel comprises the steps of providing a crude biodiesel fuel formed
by a process comprising homogeneous catalysis. The crude biodiesel
fuel is placed in an electric field to form a precipitate. The
precipitate is then removed from the crude biodiesel fuel.
[0009] The triglycerides with long chain carbon and hydrogen atoms
typically consisting of 11 to 18 carbons that may be used during
the synthesis of the biodiesel are selected from the group
consisting of vegetable oil, soybean oil, corn oil, rapeseed oil,
canola oil, peanut oil, cottonseed oil safflower oil, linseed oil,
coconut oil, animal fat, lard, tallow and mixtures thereof. The
homogeneous catalyst used during the synthesis of the biodiesel
fuel may be selected from the group consisting of sodium hydroxide,
potassium hydroxide, and sodium methoxide. The methods may be
performed in a batch process or, alternatively, a continuous
process. The electric field may have a strength of at least about
20 V/cm, or in the range of about 10 to 200 V/cm.
BRIEF DESCRIPTION OF DRAWINGS
[0010] FIG. 1 displays the exemplary transesterification reaction
of triolein to produce a biodiesel fuel.
[0011] FIG. 2a is a circuit diagram of an experimental set up, and
FIG. 2b is an illustration of the experimental set up.
[0012] FIGS. 3a and 3b are graphs showing the current vs. time
performance of the carbon 5 mm electrode and carbon 5 mm electrode
at 24 hrs.
[0013] FIG. 4 is a graph of the current vs. time for the carbon 15
mm electrode.
[0014] FIG. 5 is a graphic overlay of FTIR spectra for vegetable
oil and biodiesels.
[0015] FIG. 6 is a graphic overlay of FTIR spectra for precipitate
and biodiesel fuel purified for 24 hours.
[0016] FIGS. 7 and 8 are graphs of NMR results of the biodiesel
fuel in various phases.
[0017] FIG. 9 is the kinematic viscosity results for purified
biodiesel fuels.
DETAILED DESCRIPTION
[0018] The most common way of producing biodiesel fuel is
transesterification. In a transesterification reaction, methanol
and the catalyst are mixed together to produce a methoxide. The
methoxide is then mixed with a triglyceride and left to rest.
During this step, the glyceride chains are cut off and then
replaced with the alcohol, yielding glycerol as a viscous
by-product and methyl esters (biodiesel) which are less viscous
than the triglyceride used as the starting material. The example
reaction shown in FIG. 1 is for the triglyceride known as triolein,
one of the main components in soybean oil.
[0019] After the reaction is completed, biodiesel rises to the top
of the mixture, while the glycerol (by-product) settles to the
bottom. The biodiesel is removed and then washed with distilled
water to remove the excess catalyst and any soap formed in the
reaction. Once the purified biodiesel is heated and dried, it is
ready for commercial use.
[0020] In the present invention, it was determined that the washing
process should be considered for modification. Instead of washing
the as-produced biodiesel fraction with distilled water, electric
field assisted purification of the unwashed product was explored.
An electric field was generated between two electrodes immersed in
unwashed biodiesel to assist purification by replacing the normal
washing process in biodiesel production. Since sodium ions are
positively charged, they are attracted to the negative electrode,
while the negative component of the soap impurity is attracted to
the positive electrode, therefore removing the excess catalyst and
the soap without using distilled water.
[0021] Independent variables tested include the electric field
strength and the length of time that the electric field was being
applied. The dependent variable was the amount of sodium remaining
in the biodiesel. This dependent variable was measured by tracking
the current readings as a function of the applied voltage,
spectroscopy to provide qualitative information, viscosity and
elemental analysis to determine residual sodium. The controls were
commercial grade biodiesel (B 100) and washed biodiesel from the
stock biodiesel produced. The constants of the examples were the
environment in which the example was conducted, the materials and
method used to construct the electrodes, the voltage used in the
electric field assisted "washing" examples, the area of the
electrodes immersed in the sample, the source of unwashed biodiesel
and the instruments that were used. As demonstrated, electric field
assisted "washing" has the same effect as washing raw biodiesel
with distilled water, and electric field assisted "washing" will
clean the biodiesel faster when a stronger electrical field is
applied by shortening the distance between the electrodes while
keeping the voltage constant.
Producing Biodiesel
[0022] Biodiesel was made by reacting soybean oil with base
catalyst dissolved in methanol following a procedure based on the
one published in Make Journal--Elam, R., Making Biodiesel, Make:
Technology on Your Side 2005, 3 68-75. The stock biodiesel was
produced by combining 500 mLs of Food Lion brand soybean oil with
methoxide made from 2.5 g of Roebic.RTM. Crystal Drain Opener (100%
NaOH) dissolved in 110 mLs of Heet.RTM. (100% methanol). The oil
was warmed to 54.4.degree. C. and mixed with the methoxide in a
large plastic (PET) bottle. The mixture was shaken vigorously for
five minutes and then allowed to settle on its side overnight.
Glycerol settled out at the bottom and the as-made biodiesel
separated out on top. All samples used in the examples described
herein were taken from this batch of unwashed stock biodiesel.
Conventional Washing With Distilled Water
[0023] Approximately 50 mL of the biodiesel produced was
transferred into a separatory funnel. The biodiesel was washed by
gently mixing warm distilled water with the biodiesel. Cloudy wash
water was drained from the separatory funnel and more warm water
was added. This process was repeated until the water separated out
quickly and was clear. Once washing was completed, the biodiesel
was transferred to a beaker and gently heated until it dried and
was clear enough to read a newspaper through it. After sitting
overnight to dry more thoroughly, it was transferred into a glass
storage container.
Electric Field Assisted Washing
[0024] Electric field assisted purification of biodiesel was
carried out using two types of electrodes: copper and carbon. The
copper electrodes were constructed by stripping 5 cm of insulation
off a bell wire. The stripped wires were used as electrodes in the
experimental set-up displayed in FIG. 2b.
[0025] The carbon electrodes were constructed using fifteen sticks
of Pentel.RTM. Super Hi-Polymer.RTM. 0.9 mm thick mechanical pencil
lead held together with Loctite.RTM. Metal/Concrete Epoxy. In order
to assure uniform electrodes for each experiment, a jig was
constructed by gluing two pieces of wood on a larger piece of wood
with a gap equal to the width of the electrodes. To construct the
electrodes, a piece of aluminum foil was placed near the top part
of the jig. The fifteen sticks of pencil lead were placed in the
jig and covered with another piece of wood to insure that the
sticks were flat and even. A small amount of epoxy was then applied
using toothpicks to the top part of the sticks with the aluminum
foil underneath.
[0026] The tops of the electrodes were wrapped in aluminum foil to
ensure that the electrodes were completely conductive. An ohmmeter
was used to measure resistance to insure that the epoxy had not
made any breaks in the electrodes. Once the electrodes were
constructed, they were glued to a piece of wood that kept them 15
millimeters apart. The holder was modified with a thinner shim for
the 5 millimeter electrodes.
Circuit Configuration of Experimental Set-Up
[0027] The electrodes were connected to a Pasco Scientific Model
SF9585 High Voltage Power Supply and an ammeter used to measure the
amount of current flowing between the electrodes. The circuit
diagram for the experimental set-up is shown in FIG. 2a. The
electrodes were placed in 25 milliliters of unwashed biodiesel as
shown in FIG. 3b and the power supply was set to 50 volts. A stir
plate and Teflon coated stir bar were also used to insure that the
biodiesel circulated between the electrodes. Current was recorded
for experiments that lasted for 1.5, 4, 8, and 24 hours in
increments of 15 minutes for the first four hours and every half
hour after that.
Characterization of Biodiesel
Fourier Transform Infrared Spectroscopy
[0028] Fourier Transform Infrared Spectroscopy (FTIR) was run on a
Thermo Nicolet model number IR300 spectrometer. The sample
collection parameters were: 64 scans with a resolution of 1
cm.sup.-1 from 550-4000 cm.sup.-1.
Proton Nuclear Magnetic Resonance Spectroscopy
[0029] Proton Nuclear Magnetic Resonance Spectroscopy (.sup.1H NMR)
was run on a Bruker 300 MHz spectrometer. Each of the samples was
prepared by diluting a few drops of the specimen in deuterated
chloroform and then shaking in an NMR sample tube.
Viscosity
[0030] To obtain the kinematic viscosity of the samples, a constant
temperature water bath was set at a temperature of 40.degree. C. A
Cannon 100 Fenske viscometer was filled with 10 mL of sample using
a syringe and a 0.5 .mu.tm Teflon filter. Once the water bath was
up to the correct temperature, the viscometer was placed into the
water bath and was held by a rubber stopper for at least 10 minutes
to let the sample come to temperature. A pipet pump was used to
suck up the sample above the upper line on the lower bulb on the
right arm of the viscometer. The flow time of the sample was
measured by marking the time it took for the sample to move from
the line at the top to the line at the bottom of the lower bulb.
The time was measured by a stopwatch and recorded. The process was
repeated five times for each sample.
Elemental Analysis
[0031] Elemental analysis for sodium was performed by Midwest
Laboratories. The tests were performed using the inductively
coupled plasma method according to the DIN EN 14538:2006-09
standard.
Results
[0032] The experiment of electric field assisted wash of crude
biodiesel was first conducted using copper electrodes because they
were easy to construct and incorporate into the experimental
set-up. However, when the experiment was being conducted, the
current readings kept increasing instead of decreasing to zero as
was hypothesized. The decrease in current was expected because it
was thought that the sodium ions in the unwashed biodiesel would be
attracted to the negative electrode and the carboxylate ions of the
soap would be attracted to the positive electrode. Once there were
no conductive species in the biodiesel, current should not be able
to now flow between the electrodes. Copper tends to be reactive, so
the electrode material had to be changed to something else. To be
sure that the electric field was indeed the only thing cleaning the
biodiesel, the copper electrodes were switched to carbon
electrodes. Carbon is an inert material and will not affect the
reaction already happening with the electric field, so the results
from the experiments can be correctly interpreted.
In order to look at the effect of electric field strength on the
process of washing biodiesel, two electrode distances were
utilized. At constant voltage, the smaller the gap between the
electrodes, the stronger the electric field. The general equation
to calculate electric field strength is E=V/l, where E is the
electric field strength, V is the applied voltage, and l is the
distance between the electrodes. One set of experiments had the
electrodes 15 mm apart and the other set had the electrodes 5 mm
apart. Therefore, the electric field strengths were calculated to
be 33 V/cm and 100 V/cm respectively.
[0033] Data was initially collected at 15 and 30-minute intervals.
FIG. 3a is the overlay of current vs. time for 1.5, 4, 8 and 24
hours for the first 8 hours. It shows that current decreased for
the first 3 hours and that at around 4 hours, the current reading
fluctuated between 0 and 0.1 .mu.A. During this period, the
biodiesel also became cloudy beginning around 1.5 hours. The
1.5-hour samples stayed cloudy even after they were left to rest.
The samples processed for longer than 1.5 hours did clear up after
being left to rest; a gel precipitated out and settled at the
bottom of the container. Between 6 and 7 hours, the current
readings suddenly spiked, decreased, then continued to rise.
Although the cause of the spike is not understood at this time, it
was noted that at the end of the 24-hour experiment, some of the
gel fell off the electrodes when the electrodes were removed from
the sample.
[0034] The current recorded for the 15 mm carbon electrode behaved
similarly as the 5 mm carbon electrode as shown in FIG. 4. Current
decreased to 0 .mu.A in the first 3 hours then spiked up between 6
and 7 hours and continued to increase up to 24 hours. Gel was
observed to form during the process as well.
Fourier Transform Infrared Spectroscopy
[0035] The results for FTIR are shown in FIGS. 5 and 6. FIG. 5 is
an overlay of the spectra of vegetable oil, washed biodiesel and
commercial B100 and shows the conversion of vegetable oil to
biodiesel. The peak at 1008 cm.sup.-1 characteristics of the
asymmetric O--CH.sub.2---C group found in the triglyceride
disappeared in the biodiesel spectrum. The two peaks present for
biodiesel but not for the triglyceride were 1433 cm.sup.-1 for the
CH.sub.3-asymmetric bend and 1200 cm.sup.-1 for the O--CH.sub.3
stretch. FTIR was useful for confirming the transesterification
reaction. However, it cannot distinguish impurity levels since the
unwashed biodiesel's spectrum matched the commercial B100's
spectrum.
[0036] One spectrum in FIG. 6 represents the 24-hour carbon
electrode (5 mm) experiment and the second spectrum represents the
precipitate. The peaks on the second spectrum, 1560 cm.sup.-1 and
1400 cm.sup.-1, represent a carboxylic acid converted into its
inorganic salt. The peak at 3364 cm.sup.-1 represents bonded OH,
which also implies the presence of a carboxylic acid. This suggests
that the precipitate was the soap formed from the
transesterification side reaction. It was also observed that suds
were formed when the containers with the residue present were
rinsed with water. Therefore, it may be concluded that electric
field assisted purification removes soap.
[0037] The spectra in FIG. 7 show the conversion of soybean oil to
biodiesel. The signals at 4.1-4.4 ppm represent the glyceryl groups
of the soybean oil and the singlet at 3.7 ppm represents the methyl
ester which is biodiesel. This data agrees with the FTIR data that
biodiesel was produced. The 3.7 ppm peak is smaller for the
unwashed biodiesel than it is for the commercial B100 and washed
biodiesel, indicating the lower purity of the unwashed biodiesel.
In contrast to FTIR, NMR was able to show the presence of
impurities in the unwashed biodiesel. This suggests that NMR should
be coupled with FTIR to determine the identity of the impurities in
the commercial biodiesel production process.
[0038] The spectra in FIG. 8 are for the samples purified with the
15 mm carbon electrodes. The spectra are arranged to show the
effect of the length of time an electric field is applied to
unwashed biodiesel (bottom). At 1.5 hours, a singlet at 3.5 ppm
appears, suggesting that the carboxylic acid was present at the
same time the samples turned cloudy. In the presence of sodium
ions, carboxylic acid can be converted to carboxylase salt. As
processing time progresses, this singlet slowly disappeared until
the spectrum of the 24-hour sample matched the washed biodiesel
spectrum. This suggests that electric field assisted washing has
the same effect as washing biodiesel with distilled water, removing
the soap by precipitation.
Viscosity
[0039] The kinematic viscosity was calculated by converting the
time of the viscosity trials to seconds. The time was then
multiplied by the calibration constant for the viscometer
40.degree. C.-0.01470 mm.sup.2/s.sup.2. The results for kinematic
viscosity are shown in FIG. 9.
[0040] Kinematic viscosities were only taken for the 24-hour
samples because the other samples would not have produced accurate
readings since the samples had to be filtered before being
deposited into the viscometer. The filtration would have removed
the source of the cloudiness from the samples and not give the
kinematic viscosity of the impure samples. Filtration was necessary
to prevent the clogging of the capillary in the viscometer. The
standard deviations for these runs ranged from 0.01-0.11% over five
trials for each sample. The kinematic viscosities of each of the
samples are within the specified range of 1.9-6.0 mm.sup.2/s for
commercial biodiesel. The samples with kinematic viscosity closest
to the commercial biodiesel were those purified using the carbon
electrodes. Based on this specification, electric field assisted
purification yielded high quality biodiesel.
Elemental Analysis
[0041] Sodium analysis was required in order to determine whether
or not the electric field assisted washing removed the sodium and
the soap from the biodiesel. The results in Table 1 show that an
applied electric field removes sodium from the biodiesel.
TABLE-US-00001 TABLE 1 Sodium Analysis Results SODIUM SODIUM
CONTENT CONTENT SAMPLE (PPM) SAMPLE (PPM) Soybean oil 1.01 1.5
Hours 15 mm 8.97 Carbon B100 Commercial Not Detected 4 Hours 15 mm
3.39 Biodiesel Carbon Unwashed 28.5 8 Hours 15 mm 2.94 biodiesel
Carbon Washed biodiesel Not Detected 24 Hours 15 mm 1.64 Carbon 1.5
Hours Copper 3.13 1.5 Hours 5 mm 12.0 Carbon 3 Hours Copper 6.31 4
Hours 5 mm Carbon 6.14 24 Hours Copper Not Detected 8 Hours 5 mm
Carbon 1.82 24 Hours 5 mm 1.69 Carbon
[0042] Each set of carbon samples show a decrease of sodium as a
function of time. There was a dramatic reduction in sodium content
after only 1.5 hours of processing with an electric field. The
results also imply that the field strength was not directly related
to rate of removal of sodium since the rates at which sodium were
reduced using 15 mm or 5 mm electrodes were similar. The data for
samples purified with copper electrodes were consistent with the
current readings and the NMR data. The sodium content increased as
time increased, but the sodium was eventually removed after 24
hours. This behavior was not anticipated and suggests that the
copper electrodes may have been involved in a chemical reaction.
Electric field assisted washing may be more complicated for the
reactive copper electrodes than for the inert carbon
electrodes.
Summary And Conclusion
[0043] This study showed that it is possible to remove soap from
biodiesel without using water by applying an electric field using
inert carbon electrodes. The electrodes provided a means to remove
soap by attracting sodium and carboxylate ions to the oppositely
charged electrodes. Once the ions have been attracted. they clump
together and precipitate out of the biodiesel, leaving behind clean
biodiesel. This process was made possible with field strengths in
the range of 33-100 V/cm, which is much lower than the field
strengths required to transesterify oil by electro-catalysis.
Alternatively, the field strength is at least about 20 V/cm, or
still further, in the range of about 10 V/cm to 200 V/cm.
[0044] It is believed that the DC (and by inference sufficiently
low frequency AC) conductivities are bounded by 1.8.times.10.sup.-8
to 2.3.times.10.sup.-6 Mhos/m. The above conductivities relate to
the ionic byproducts of the synthesis reaction, presumably the
sodium and carboxylate ions. Of course, different conductivities
would apply to other reaction products including ionic, polar and
nonpolar components. Depending on the biodiesel reaction
ingredients, different conductivities of reaction products will
exist and must be factored in the design and operation of an
appropriate electric field.
[0045] As is evident from the foregoing, the reaction rate in this
purification process is such that substantial electrode area will
be required to make the process useful at any large scale. The
foregoing examples are all batch type examples. It is also possible
to have a continuous process. Potential constructions that could be
used in a continuous process include a trough or tube for crude
biodiesel to flow through with multiple sets of electrodes running
parallel or perpendicular to the tube/trough. Alternatively, a
trough/tube constructed from electrode material (e.g., graphite, or
other chemically inert material) which acts as one electrode and
another electrode through the center of the trough/tube to act as a
second electrode. This allows the continuous application of an
electric field as crude biodiesel flows through.
[0046] Processing volume can be adjusted by having multiple
troughs/tubes in parallel branching from the crude biodiesel source
or in series from the source.
[0047] Mechanisms for moving gelled precipitate from an electric
field assisted purification system include the use of a scrape or
squeegee to clean soap residue off of the electrodes at periodic
times. Automated wipers could be used. The precipitate could also
be removed by applying an electrical switching sequence to the
electrodes. Filters could also be used in one or more locations in
the process to otherwise filter out the precipitate byproduct.
[0048] The triglycerides that may be used in connection with this
biodiesel synthesis and subsequent purification process include the
following: triglycerides with long chain carbon and hydrogen atoms
typically consisting of 11 to 18 carbon atoms, vegetable oil,
soybean oil, rapeseed oil, corn oil, canola oil, peanut oil,
cottonseed oil, safflower oil, linseed oil, coconut oil, animal
fat. lard, tallow, and mixtures thereof.
[0049] Also, sodium hydroxide is identified herein for use as a
homogeneous catalyst. Other catalysts that may be used include
potassium hydroxide, and sodium methoxide.
[0050] Although the present method of electric field assisted
purification is discussed alone, it will be apparent to those of
skill in the art that an electric field may be used with
traditional distilled water rinsing to purify crude biodiesel. The
use of an electric field in parallel or in series with distilled
water rinsing could reduce presumably significantly, the amount of
distilled water necessary to end up with acceptably purified
biodiesel fuel.
[0051] The corresponding structures, materials, acts, and
equivalents of all means or step plus function elements in the
claims below are intended to include any structure, material, or
act for performing the function in combination with other claimed
elements as specifically claimed. The description of the present
invention has been presented for purposes of illustration and
description, but is not intended to be exhaustive or limited to the
invention in the form disclosed. Many modifications and variations
will be apparent to those of ordinary skill in the art without
departing from the scope and spirit of the invention. The
experiments were chosen and described in order to best explain the
principles of the invention and the practical application, and to
enable others of ordinary skill in the art to understand the
invention for various embodiments with various modifications as are
suited to the particular use contemplated.
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